remove gconvert_uri_to_filename() and use url_unescape_string() instead.

remove gconvert_uri_to_filename() and use url_unescape_string() instead.
reasons:
* gconvert strdup()s the original string, but it may exit without returning or freeing it.
* gconvert returns the original pointer when no % escaping is done. It is then free()ed and used in that state.
* gconvert doesn't consider that % may be at the end of the string and could continue parsing past the end.
* gconvert would try to free() pointer that iconv() have modified.
* gconvert would try to convert filenames from utf-8 to iso8859-1.
  Seems like no other DnD programs convert to utf-8 and/or honors CHARSET.
  Not converting seems to work best. Fix it if problem arises.

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@24106 b3059339-0415-0410-9bf9-f77b7e298cf2