glx: Avoid calling __glXInitialize() in driReleaseDrawables().

glx: Avoid calling __glXInitialize() in driReleaseDrawables().

This fixes a regression introduced by commit
a26121f37530619610a78a5fbe5ef87e44047fda (fd.o bug #39219).

Since the __glXInitialize() call should be unnecessary anyway, this is
probably a nicer fix for the original problem too.

NOTE: This is a candidate for the 7.10 and 7.11 branches.

Signed-off-by: Henri Verbeet <hverbeet@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Tested-by: padfoot@exemail.com.au
(cherry picked from commit 0f20e2e18f902b4319851643e1775a18c2aacb3d)