llvmpipe: fix fragdata/lastfragdata heuristic a bit more.

This heuristic broke when zmike lowered fragcolor using NIR,

This fixes a regression in:
dEQP-GLES31.functional.shaders.framebuffer_fetch.basic.last_frag_data

Fixes: db1371cce1 ("llvmpipe: fix handling of unused color attachments")
Acked-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24435>

src/gallium/drivers/llvmpipe/lp_state_fs.c

@@ -1186,8 +1186,7 @@ generate_fs_loop(struct gallivm_state *gallivm,
       if ((shader->info.base.output_semantic_name[attrib]
            == TGSI_SEMANTIC_COLOR) &&
            ((cbuf < key->nr_cbufs) || (cbuf == 1 && dual_source_blend))) {
-         if (cbuf == 0 &&
-             shader->info.base.properties[TGSI_PROPERTY_FS_COLOR0_WRITES_ALL_CBUFS]) {
+         if (cbuf == 0) {
             /* XXX: there is an edge case with FB fetch where gl_FragColor and
              * gl_LastFragData[0] are used together. This creates both
              * FRAG_RESULT_COLOR and FRAG_RESULT_DATA* output variables. This