Provide only UTF-8 translations for VIM and use UTF-8 to generate other encodings

 Several .po files exist with different encodings, like SJIS. CP936, etc. Those are completely useless for Linux users as translations get converted with iconv into the encoding the user is using anyways. We prefer to use UTF-8 for import into Launchpad Rosetta. So, if there are UTF-8 encoded .po files available in addition to other encodings, please rename the .UTF-8.po files to .po and remove the other encodings.
Affected files in the vim package:

 cs.cp1250.po -> remove
 ja.sjis.po -> remove
 pl.cp1250.po -> remove
 ru.cp1251.po -> remove
 sk.cp1250.po -> remove
 uk.cp1251.po -> remove
 zh_CN.cp936.po -> remove

 pl.UTF-8.po -> rename to pl.po and overwrite the existing one
 zh_CN.UTF-8.po -> rename to zh_CN.po and overwrite the existing one
 zh_TW.UTF-8.po -> rename to zh_TW.po and overwrite the existing one