mesa: Replace gl_extensions::EXT_texture3D with ::dummy_true

Mesa unconditionally sets this driver flag to true in
_mesa_init_extensions(). There is therefore no need for
the driver to communicate support for this extension.
Replace the driver capability flag with ::dummy_true.

Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>

src/glsl/glsl_parser_extras.cpp

@@ -634,7 +634,7 @@ static const _mesa_glsl_extension _mesa_glsl_supported_extensions[] = {
     */
    EXT(OES_EGL_image_external,         false, true,      OES_EGL_image_external),
    EXT(OES_standard_derivatives,       false, true,      OES_standard_derivatives),
-   EXT(OES_texture_3D,                 false, true,      EXT_texture3D),
+   EXT(OES_texture_3D,                 false, true,      dummy_true),
    EXT(OES_texture_storage_multisample_2d_array, false, true, ARB_texture_multisample),
 
    /* All other extensions go here, sorted alphabetically.