Python 3: Use 'filename: learnpython*.py' (no '3')

Before renaming, Python 3 filenames were 'learnpython3*.py'.

This commit removes the '3' part from the filename.

To verify that the filenames were named consistently across
translations prior to this commit, and to change this:

```
ack -H 'filename:' python.html.markdown
find . -name "python-*.markdown" -exec ack -H 'filename:' {} \;

sed -i 's/^filename: learnpython3/filename: learnpython/' \
  python.html.markdown

find . -name "python-*.markdown" -exec \
  sed -i 's/^filename: learnpython3/filename: learnpython/' {} \;
```

ar-ar/python-ar.html.markdown

@@ -11,7 +11,7 @@ contributors:
 translators:
     - ["Ahmad Hegazy", "https://github.com/ahegazy"]
 lang: ar-ar
-filename: learnpython3-ar.py
+filename: learnpython-ar.py
 ---
 
 لقد أُنشئت لغة البايثون بواسطة جايدو ڤان روسم في بداية التسعينات. هي الأن أحد أشهر اللغات الموجودة. 

de-de/python-de.html.markdown

@@ -5,7 +5,7 @@ contributors:
 translators:
     - ["kultprok", "http:/www.kulturproktologie.de"]
     - ["matthiaskern", "https://github.com/matthiaskern"]
-filename: learnpython3-de.py
+filename: learnpython-de.py
 lang: de-de
 ---
 

el-gr/python-gr.html.markdown

@@ -8,7 +8,7 @@ contributors:
     - ["evuez", "http://github.com/evuez"]
     - ["Rommel Martinez", "https://ebzzry.io"]
     - ["Roberto Fernandez Diaz", "https://github.com/robertofd1995"]
-filename: learnpython3-gr.py
+filename: learnpython-gr.py
 lang: el-gr
 ---
 

es-es/python-es.html.markdown

@@ -5,7 +5,7 @@ contributors:
 translators:
     - ["Camilo Garrido", "http://twitter.com/hirohope"]
 lang: es-es
-filename: learnpython3-es.py
+filename: learnpython-es.py
 ---
 
 Python fue creado por Guido Van Rossum en el principio de los 90'. Ahora es uno

fr-fr/python-fr.html.markdown

@@ -8,7 +8,7 @@ contributors:
 translators:
     - ["Gnomino", "https://github.com/Gnomino"]
     - ["Julien M'Poy", "http://github.com/groovytron"]
-filename: learnpython3-fr.py
+filename: learnpython-fr.py
 lang: fr-fr
 ---
 

it-it/python-it.html.markdown

@@ -1,6 +1,6 @@
 ---
 language: Python
-filename: learnpython3-it.py
+filename: learnpython-it.py
 contributors:
     - ["Louie Dinh", "http://pythonpracticeprojects.com"]
     - ["Steven Basart", "http://github.com/xksteven"]

ja-jp/python-jp.html.markdown

@@ -11,7 +11,7 @@ contributors:
 translators:
     - ["kakakaya", "https://github.com/kakakaya"]
     - ["Ryota Kayanuma", "https://github.com/PicoSushi"]
-filename: learnpython3-jp.py
+filename: learnpython-jp.py
 lang: ja-jp
 ---
 

pt-br/python-pt.html.markdown

@@ -9,7 +9,7 @@ translators:
     - ["Paulo Henrique Rodrigues Pinheiro", "http://www.sysincloud.it"]
     - ["Monique Baptista", "https://github.com/bfmonique"]
 lang: pt-br
-filename: learnpython3-pt.py
+filename: learnpython-pt.py
 ---
 
 Python foi criada por Guido Van Rossum nos anos 1990. Ela é atualmente uma

python.html.markdown

@@ -9,7 +9,7 @@ contributors:
     - ["Rommel Martinez", "https://ebzzry.io"]
     - ["Roberto Fernandez Diaz", "https://github.com/robertofd1995"]
     - ["caminsha", "https://github.com/caminsha"]
-filename: learnpython3.py
+filename: learnpython.py
 ---
 
 Python was created by Guido van Rossum in the early 90s. It is now one of the most popular

ru-ru/python-ru.html.markdown

@@ -6,7 +6,7 @@ contributors:
     - ["Steven Basart", "http://github.com/xksteven"]
 translators:
     - ["Andre Polykanine", "https://github.com/Oire"]
-filename: learnpython3-ru.py
+filename: learnpython-ru.py
 ---
 
 Язык Python был создан Гвидо ван Россумом в начале 90-х. Сейчас это один из

tr-tr/python-tr.html.markdown

@@ -8,7 +8,7 @@ contributors:
 translators:
     - ["Eray AYDIN", "http://erayaydin.me/"]
 lang: tr-tr
-filename: learnpython3-tr.py
+filename: learnpython-tr.py
 ---
 
 Python,90ların başlarında Guido Van Rossum tarafından oluşturulmuştur. En popüler olan dillerden biridir. Beni Python'a aşık eden sebep onun syntax beraklığı. Çok basit bir çalıştırılabilir söz koddur.

vi-vn/python-vi.html.markdown

@@ -1,6 +1,6 @@
 ---
 language: Python
-filename: learnpython3-vi.py
+filename: learnpython-vi.py
 contributors:
     - ["Louie Dinh", "http://pythonpracticeprojects.com"]
     - ["Steven Basart", "http://github.com/xksteven"]

zh-cn/python-cn.html.markdown

@@ -6,7 +6,7 @@ contributors:
     - ["Andre Polykanine", "https://github.com/Oire"]
 translators:
     - ["Geoff Liu", "http://geoffliu.me"]
-filename: learnpython3-cn.py
+filename: learnpython-cn.py
 lang: zh-cn
 ---