Unused since https://gitlab.gnome.org/GNOME/mutter/merge_requests/932
AFAICT.
As a bonus, gets rid of these compiler warnings:
../cogl/cogl/cogl-pipeline-layer-state.c: In function ‘cogl_pipeline_get_layer_min_filter’:
../cogl/cogl/cogl-pipeline-layer-state.c:1279:10: warning: ‘min_filter’ may be used uninitialized [-Wmaybe-uninitialized]
1279 | return min_filter;
| ^~~~~~~~~~
../cogl/cogl/cogl-pipeline-layer-state.c:1274:22: note: ‘min_filter’ was declared here
1274 | CoglPipelineFilter min_filter;
| ^~~~~~~~~~
../cogl/cogl/cogl-pipeline-layer-state.c: In function ‘cogl_pipeline_get_layer_mag_filter’:
../cogl/cogl/cogl-pipeline-layer-state.c:1291:10: warning: ‘mag_filter’ may be used uninitialized [-Wmaybe-uninitialized]
1291 | return mag_filter;
| ^~~~~~~~~~
../cogl/cogl/cogl-pipeline-layer-state.c:1287:22: note: ‘mag_filter’ was declared here
1287 | CoglPipelineFilter mag_filter;
| ^~~~~~~~~~
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2757>