mesa: Remove PROGRAM_ENV_PARAM enum.

This has been replaced with referring to env parameters using
PROGRAM_STATE_VAR and _mesa_load_state_parameters.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/program/program.c

@@ -909,9 +909,6 @@ _mesa_valid_register_index(const struct gl_context *ctx,
    case PROGRAM_TEMPORARY:
       return index >= 0 && index < (GLint) c->MaxTemps;
 
-   case PROGRAM_ENV_PARAM:
-      return index >= 0 && index < (GLint) c->MaxEnvParams;
-
    case PROGRAM_UNIFORM:
    case PROGRAM_STATE_VAR:
       /* aka constant buffer */