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/proto_test.go b/cc/proto_test.go
index 4f0de78..f8bbd26 100644
--- a/cc/proto_test.go
+++ b/cc/proto_test.go
@@ -29,7 +29,7 @@
 			srcs: ["a.proto"],
 		}`)
 
-		proto := ctx.ModuleForTests("libfoo", "android_arm_armv7-a-neon_core_shared").Output("proto/a.pb.cc")
+		proto := ctx.ModuleForTests("libfoo", "android_arm_armv7-a-neon_shared").Output("proto/a.pb.cc")
 
 		if cmd := proto.RuleParams.Command; !strings.Contains(cmd, "--cpp_out=") {
 			t.Errorf("expected '--cpp_out' in %q", cmd)
@@ -53,7 +53,7 @@
 
 		buildOS := android.BuildOs.String()
 
-		proto := ctx.ModuleForTests("libfoo", "android_arm_armv7-a-neon_core_shared").Output("proto/a.pb.cc")
+		proto := ctx.ModuleForTests("libfoo", "android_arm_armv7-a-neon_shared").Output("proto/a.pb.cc")
 		foobar := ctx.ModuleForTests("protoc-gen-foobar", buildOS+"_x86_64")
 
 		cmd := proto.RuleParams.Command