feat(provider)!: remove support for python2 and python3.[3-5]

These versions of python has reached End-of-life. getting rid
of python2 support removes a lot of logic to support two
incompatible python versions in the same version.

src/nvim/options.lua

@@ -1846,7 +1846,7 @@ return {
       type='number', scope={'global'},
       secure=true,
       varname='p_pyx',
-      defaults={if_true=0}
+      defaults={if_true=3}
     },
     {
       full_name='quickfixtextfunc', abbreviation='qftf',