Replace touch -a with comment

Bug: 278060169
Test: m
Change-Id: Ie5ad1b5c6cf335cc3de641fd76a76bfa5f3f79cb
diff --git a/core/main.mk b/core/main.mk
index 36bfbfa..497fac6 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -47,9 +47,9 @@
 $(KATI_obsolete_var FILE_NAME_TAG,https://android.googlesource.com/platform/build/+/master/Changes.md#FILE_NAME_TAG)
 
 $(BUILD_NUMBER_FILE):
-	touch -a $@
+	# empty rule to prevent dangling rule error for a file that is written by soong_ui
 $(BUILD_HOSTNAME_FILE):
-	touch -a $@
+	# empty rule to prevent dangling rule error for a file that is written by soong_ui
 
 .KATI_RESTAT: $(BUILD_NUMBER_FILE)
 .KATI_RESTAT: $(BUILD_HOSTNAME_FILE)