Remove symbol versioning from DSO

This removes GNU symbol versioning from the dynamic shared object.

Note that this still uses the GNU version file. The alternative would be to use -export-symbols symfile (which requires to explicitly list all symbols) or -export-symbols-regex regex (which makes it necessary to use a regex instead of simple wildcards, but may be not that bad if we ignore wlr_signal_emit_safe's case and go with something like ^_?wlr_.*). See for instance https://gitlab.com/axil/gnutls/commit/6c2512405eabc83fe64b72ca81d4c1989a9e0e22