libtextstyle: Remove unused code for exporting variables from Windows DLLs.
Here we use the third approach listed in gettext-tools/woe32dll/export.h, not
the fourth approach.
* libtextstyle/Makefile.am: Remove code that was never enabled.
* libtextstyle/lib/Makefile.am: Likewise.
* libtextstyle/configure.ac (false): Remove conditional.
