glsl: tidy up PostDepthCoverage shader field

There is no reason for this to be in the shared gl_shader_info or
to copy it to gl_program at the end of linking (its already there).

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/compiler/glsl/glsl_parser_extras.cpp

@@ -1816,7 +1816,7 @@ set_shader_inout_layout(struct gl_shader *shader,
          state->ARB_fragment_coord_conventions_enable;
       shader->EarlyFragmentTests = state->fs_early_fragment_tests;
       shader->info.InnerCoverage = state->fs_inner_coverage;
-      shader->info.PostDepthCoverage = state->fs_post_depth_coverage;
+      shader->PostDepthCoverage = state->fs_post_depth_coverage;
       shader->BlendSupport = state->fs_blend_support;
       break;