mesa: don't handle STATE_* enums in fetch_state that don't do anything

_mesa_program_state_flags() already reports invalid state flags. fetch_state is
always called after that.

Reviewed-by: Zoltán Böszörményi <zboszor@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8183>

src/mesa/program/prog_statevars.c

@@ -665,20 +665,6 @@ fetch_state(struct gl_context *ctx, const gl_state_index16 state[],
          COPY_4V(value, ctx->Transform._ClipUserPlane[plane]);
       }
       return;
-
-   case STATE_INTERNAL_DRIVER:
-      /* Internal driver state */
-      return;
-
-   case STATE_NOT_STATE_VAR:
-      /* Most likely PROGRAM_CONSTANT. This only happens in rare cases, e.g.
-       * ARB_vp with ARL, which can't sort parameters by type.
-       */
-      return;
-
-   default:
-      unreachable("Invalid state in _mesa_fetch_state");
-      return;
    }
 }