Remove Malayalam; support for it isn't ready

There are Unicode normalization problems with Malayalam -- as best I understand
it, Unicode simply neglected to include normalization forms for Malayalam "chillu"
characters even though they changed how they're represented in Unicode 5.1 and
again in Unicode 9.

The result is that words that print the same end up with multiple entries, with
different codepoint sequences that don't normalize to each other.

I certainly don't know how to resolve this, and it would need to be resolved to
have something that we could reasonably call Malayalam word frequencies.

README.md

@@ -193,7 +193,6 @@ least 3 different sources of word frequencies:
     Lithuanian  lt      3  -      │ Yes   Yes   -     -     Yes   -     -     -
     Macedonian  mk      5  Yes    │ Yes   Yes   Yes   -     Yes   Yes   -     -
     Malay       ms      3  -      │ Yes   Yes   -     -     -     Yes   -     -
-    Malayalam   ml      3  -      │ Yes   Yes   -     -     -     Yes   -     -
     Norwegian   nb [2]  5  Yes    │ Yes   Yes   -     -     Yes   Yes   Yes   -
     Persian     fa      4  -      │ Yes   Yes   -     -     Yes   Yes   -     -
     Polish      pl      6  Yes    │ Yes   Yes   Yes   -     Yes   Yes   Yes   -

tests/test_general.py

@@ -83,7 +83,6 @@ def test_most_common_words():
     assert get_most_common('lt') == 'ir'
     assert get_most_common('lv') == 'un'
     assert get_most_common('mk') == 'на'
-    assert get_most_common('ml') == 'ഒരു'
     assert get_most_common('ms') == 'yang'
     assert get_most_common('nb') == 'i'
     assert get_most_common('nl') == 'de'