Remove codepage macros. Remove redundant BIG5 macros.

Remove codepage macros. Remove redundant BIG5 macros.
(dumpglyphs): Move definitions out of block containing goto.
Remove redundant code for BIG5.
Use w32_codepage_for_font instead of
w32_codepage_for_charset.  Add cast to int where float
operation is assigned to int.
(Vw32_charset_to_codepage_alist): New variable.
(w32_codepage_for_charset): Removed.
(w32_codepage_for_font): New function, replacing
w32_codepage_for_charset.
(syms_of_w32term): Add and initialize
w32-charset-to-codepage-alist.