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/java/java_test.go b/java/java_test.go
index f4b92e3..4a549e6 100644
--- a/java/java_test.go
+++ b/java/java_test.go
@@ -1177,7 +1177,7 @@
 	ctx.ModuleForTests("foo"+sdkDocsSuffix, "android_common")
 	ctx.ModuleForTests("foo"+sdkDocsSuffix+sdkSystemApiSuffix, "android_common")
 	ctx.ModuleForTests("foo"+sdkDocsSuffix+sdkTestApiSuffix, "android_common")
-	ctx.ModuleForTests("foo"+sdkXmlFileSuffix, "android_arm64_armv8-a_core")
+	ctx.ModuleForTests("foo"+sdkXmlFileSuffix, "android_arm64_armv8-a")
 	ctx.ModuleForTests("foo.api.public.28", "")
 	ctx.ModuleForTests("foo.api.system.28", "")
 	ctx.ModuleForTests("foo.api.test.28", "")