awesome: Remove $LD_LIBRARY_PATH handling

I have no idea why gobjectIntrospection even was in here. The only
library in there, libgirepository-1.0.so, is not used by awesome. It is
only used by lgi.so and that means it should be found via its RPATH.

The Pango path is not needed in $LD_LIBRARY_PATH ever since
gobjectIntrospection started patching .typelib files with absolute
paths. Relevant commits are 36bef2b2 from 2014
("gobject-introspection: refer to shlibs with absolute paths in
typelibs") and c420de6b from 2016 ("gobject-introspection: Fix
patching shared objects").

The above patches did not work for cairo, because cairo's typelib is a
bit "special". However, this was fixed by e44038bc some days ago
("gobjectIntrospection: use absolute path for cairo GIR").

Thus, setting $GI_TYPELIB_PATH is enough so that all needed libraries
are found.

Fixes: https://github.com/NixOS/nixpkgs/issues/14164


Signed-off-by: Uli Schlachter <psychon@znc.in>