Remove extra return value from testApex

The config value returned by testApex is no longer used, remove it.

Test: go test  ./apex
Change-Id: I9327c1b139c17305454fb0a111e41456cdcaebc3

apex/boot_image_test.go

@@ -28,7 +28,7 @@ import (
 // modules from the ART apex.
 
 func TestBootImages(t *testing.T) {
-	ctx, _ := testApex(t, `
+	ctx := testApex(t, `
 		java_sdk_library {
 			name: "foo",
 			srcs: ["b.java"],
@@ -180,7 +180,7 @@ func withFrameworkBootImageJars(bootJars ...string) func(fs map[string][]byte, c
 }
 
 func TestBootImageInApex(t *testing.T) {
-	ctx, _ := testApex(t, `
+	ctx := testApex(t, `
 		apex {
 			name: "myapex",
 			key: "myapex.key",