Allow discarding lines from patch directly

I always press 'd' in the patch building view, expecting that I can do
exactly what I can do in the staging view, to find out I need to go
space -> ctrl+p -> d and I think it's time to honour the muscle memory
and support this convenience keybinding.

pkg/integration/tests/test_list.go

@@ -328,6 +328,7 @@ var tests = []*components.IntegrationTest{
 	patch_building.ApplyInReverseWithConflict,
 	patch_building.ApplyWithModifiedFileConflict,
 	patch_building.ApplyWithModifiedFileNoConflict,
+	patch_building.DiscardLinesFromCommit,
 	patch_building.EditLineInPatchBuildingPanel,
 	patch_building.MoveRangeToIndex,
 	patch_building.MoveToEarlierCommit,