Remove reference to PRODUCT-*

The code still needs to exist, but for buildspec.mk files, not the
PRODUCT-* arguments.

Test: none
Change-Id: I60c6044ab2d1627af7e6e2e8831b77d9db12aa55

ui/build/dumpvars.go

@@ -169,7 +169,7 @@ func runMakeProductConfig(ctx Context, config Config) {
 	// Variables to export into the environment of Kati/Ninja
 	exportEnvVars := []string{
 		// So that we can use the correct TARGET_PRODUCT if it's been
-		// modified by PRODUCT-*/APP-* arguments
+		// modified by a buildspec.mk
 		"TARGET_PRODUCT",
 		"TARGET_BUILD_VARIANT",
 		"TARGET_BUILD_APPS",