Remove useless casts to (void *)

Many of them just seem to have been copied around for no real reason.
Their presence causes (small) risks of hiding actual type mismatches
or silently discarding qualifiers

Discussion: https://www.postgresql.org/message-id/flat/461ea37c-8b58-43b4-9736-52884e862820@eisentraut.org

src/backend/access/spgist/spginsert.c

@@ -122,7 +122,7 @@ spgbuild(Relation heap, Relation index, IndexInfo *indexInfo)
 											  ALLOCSET_DEFAULT_SIZES);
 
 	reltuples = table_index_build_scan(heap, index, indexInfo, true, true,
-									   spgistBuildCallback, (void *) &buildstate,
+									   spgistBuildCallback, &buildstate,
 									   NULL);
 
 	MemoryContextDelete(buildstate.tmpCtx);

src/backend/access/spgist/spgutils.c

@@ -279,7 +279,7 @@ spgGetCache(Relation index)
 			UnlockReleaseBuffer(metabuffer);
 		}
 
-		index->rd_amcache = (void *) cache;
+		index->rd_amcache = cache;
 	}
 	else
 	{