intel: Drop intelFlush()

Now that intel_flush() deosn't use the needs_mi_flush argument, we can
finally drop one of the two flush functions.

src/mesa/drivers/dri/intel/intel_regions.c

@@ -111,7 +111,7 @@ debug_backtrace(void)
 GLubyte *
 intel_region_map(struct intel_context *intel, struct intel_region *region)
 {
-   intelFlush(&intel->ctx);
+   intel_flush(&intel->ctx);
 
    _DBG("%s %p\n", __FUNCTION__, region);
    if (!region->map_refcount++) {