Unify installDirOnHost and installDirOnDevice.

These two fields never do what they are described to do. This CL unifies
them to avoid the confusion.

Bug: 280440941
Test: m
Change-Id: I3652d73a50832a2e494d9f5cae750f5fc38293b4
diff --git a/java/testing.go b/java/testing.go
index 4ff2aa4..6671bf0 100644
--- a/java/testing.go
+++ b/java/testing.go
@@ -610,9 +610,9 @@
 	})
 }
 
-// Sets the value of `installDirOnDevice` of the boot image config with the given name.
+// Sets the value of `installDir` of the boot image config with the given name.
 func FixtureSetBootImageInstallDirOnDevice(name string, installDir string) android.FixturePreparer {
 	return FixtureModifyBootImageConfig(name, func(config *bootImageConfig) {
-		config.installDirOnDevice = installDir
+		config.installDir = installDir
 	})
 }