Bug 1612973 - allow opaque images to use the fast image shader. r=nical

Differential Revision: https://phabricator.services.mozilla.com/D61508

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/6deaa5a356b2106c4393357b365280ca54ca7d22

webrender/src/shade.rs

@@ -936,8 +936,7 @@ impl Shaders {
                     }
                     BrushBatchKind::Image(image_buffer_kind) => {
                         if features.contains(BatchFeatures::ANTIALIASING) ||
-                            features.contains(BatchFeatures::REPETITION) ||
-                            !features.contains(BatchFeatures::ALPHA_PASS) {
+                            features.contains(BatchFeatures::REPETITION) {
 
                             self.brush_image[image_buffer_kind as usize]
                                 .as_mut()