glsl: Rely on talloc_autofree_context() instead of trying to free on our own.

glsl: Rely on talloc_autofree_context() instead of trying to free on our own.

Because the static types talloc their names at dlopen time,
talloc_freeing the types at DRI driver screen teardown means that if
the screen gets brought back up again, the names will point at freed
memory.  talloc_autofree_context() exists to do just what we want
here: Free memory referenced across the program's lifetime so that we
avoid noise in memory leak checkers.

Fixes: bug #29722 (assertion failure in unigine).