Don't use long deprecated and now removed pangox library in wxX11 any more.

Use pangoxft only now.

Also remove the apparently unused src/x11/pangox11.cpp file, only
src/x11/pango_x.cpp seems to be used (and this one only by being included in
src/x11/dcclient.cpp).

Closes #15482.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74981 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775