etnaviv: drop obsolete question about alpha/stencil test interaction

There's a few things that will prevent enabling the more efficient
PE_COLOR_FORMAT_OVERWRITE mode, but pixel dicard due to alpha or
stencil testing isn't one of those conditions, as this behaves the
same way as pixel discard due to a failed depth test.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35704>

src/gallium/drivers/etnaviv/etnaviv_zsa.c

@@ -120,6 +120,5 @@ etna_zsa_state_create(struct pipe_context *pctx,
          VIVS_PE_STENCIL_CONFIG_EXT2_WRITE_MASK_BACK(stencil_back->writemask);
    }
 
-   /* XXX does alpha/stencil test affect PE_COLOR_FORMAT_OVERWRITE? */
    return cs;
 }