gl: drop incorrect pkg-config file for glvnd

Akin to 1a25980c46 ("egl: drop incorrect pkg-config file for
glvnd") and b01524fff0 ("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>
(cherry picked from commit a1de3011f3)

src/meson.build

@@ -106,22 +106,12 @@ endif
 
 # This must be after at least mesa, glx, and gallium, since libgl will be
 # defined in one of those subdirs depending on the glx provider.
-if with_glx != 'disabled'
-  # If using glvnd the pkg-config header should not point to GL_mesa, it should
-  # point to GL. glvnd is only available on unix like platforms so adding -l
-  # should be safe here
-  # TODO: in the glvnd case glvnd itself should really be providing this.
-  if with_glvnd
-    _gl = '-L${libdir} -lGL'
-  else
-    _gl = libgl
-  endif
-
+if with_glx != 'disabled' and not with_glvnd
   pkg.generate(
     name : 'gl',
     description : 'Mesa OpenGL Library',
     version : meson.project_version(),
-    libraries : _gl,
+    libraries : libgl,
     libraries_private : gl_priv_libs,
     requires_private : gl_priv_reqs,
     variables : ['glx_tls=yes'],