gl: drop incorrect pkg-config file for glvnd

gl: drop incorrect pkg-config file for glvnd

Akin to 1a25980c469b38d2c645 ("egl: drop incorrect pkg-config file for
glvnd") and b01524fff05eef66e8cd ("meson: don't build libGLES*.so with
GLVND") , removes a pkg-config file that shouldn't have been there in
the first place, but was needed because of that GLVND bug.

Now that the glvnd bug has been fixed, it was apparent that this gl.pc
pkg-config file was forgotten to be removed, so let's do just that :)

Suggested-by: Matt Turner <mattst88@gmail.com>
Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>