Posixify the locales name for variants

For all locales with variants:

• if no ambiguity on the locale (only one variant) just use the regular name
• if ambiguity, pick one as default and append @<variant> to the others respecting POSIX

As a result:

• All the 3 components locales added recently are renamed to the usual 2 components version for all but sr_RS.UTF-8
• Set sr_RS.UTF-8 to the cyrillic variant
• Add sr_RS.UTF-8@latin
• Remove the symlinks aliases they were created to represent the 2 components version as aliasas and are now useless
• Update the OptionalObsoleteFiles.inc and ObsoleteFiles.inc to reflect those changes

Discussed with: ache@
Approved by: re@ (gjb)