Fix bootclasspath for host variants of java_library modules

The partial hostdex support was causing the host variant of
java_library modules to depend on core-oj and core-libart,
which caused the tagsoup jar to use the wrong
java.lang.System.arraycopy signature.  Remove the hostdex
code that was causing the problem, and add a test.

Test: java_test.go
Change-Id: I4f7b1f29c99aae328ba19b042538d9d35544aa43
diff --git a/java/java.go b/java/java.go
index eb94806..3eadbb6 100644
--- a/java/java.go
+++ b/java/java.go
@@ -285,9 +285,7 @@
 				ctx.AddDependency(ctx.Module(), bootClasspathTag, sdkDep.module)
 			}
 		} else {
-			if j.deviceProperties.Dex {
-				ctx.AddDependency(ctx.Module(), bootClasspathTag, config.DefaultBootclasspathLibraries...)
-			}
+			// TODO(ccross): add hostdex support
 		}
 	}
 	ctx.AddDependency(ctx.Module(), libTag, j.properties.Libs...)