Use empty string for core image variant

Use the empty string for the core image variant so that modules
added to imageMutator do not change their build directory.

Bug: 142286466
Test: m checkbuild
Change-Id: Ida4534d9a4d6176236aaa480fed359ce27acfaa1
Merged-In: Ida4534d9a4d6176236aaa480fed359ce27acfaa1
(cherry picked from commit 72d685ee7f45e5393be44ae4159edf083ac918de)
diff --git a/cc/genrule_test.go b/cc/genrule_test.go
index 9f159e5..785e3e1 100644
--- a/cc/genrule_test.go
+++ b/cc/genrule_test.go
@@ -74,13 +74,13 @@
 		t.Fatal(errs)
 	}
 
-	gen := ctx.ModuleForTests("gen", "android_arm_armv7-a-neon_core").Output("out_arm")
+	gen := ctx.ModuleForTests("gen", "android_arm_armv7-a-neon").Output("out_arm")
 	expected := []string{"foo"}
 	if !reflect.DeepEqual(expected, gen.Inputs.Strings()) {
 		t.Errorf(`want arm inputs %v, got %v`, expected, gen.Inputs.Strings())
 	}
 
-	gen = ctx.ModuleForTests("gen", "android_arm64_armv8-a_core").Output("out_arm64")
+	gen = ctx.ModuleForTests("gen", "android_arm64_armv8-a").Output("out_arm64")
 	expected = []string{"bar"}
 	if !reflect.DeepEqual(expected, gen.Inputs.Strings()) {
 		t.Errorf(`want arm64 inputs %v, got %v`, expected, gen.Inputs.Strings())