.gn: remove no_stamp_files

This is not necessary after https://crrev.com/c/5840665.

Bug: 42440099
Change-Id: I7d52937eff8d13bfe8d60ed8e097edc3a77b7ac8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5836546
Reviewed-by: Junji Watanabe <jwata@google.com>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1351882}

.gn

@@ -12,10 +12,6 @@ buildconfig = "//build/config/BUILDCONFIG.gn"
 # for python3.exe and python3.bat.
 script_executable = "python3"
 
-# This reduces the number of stamp actions, use phony rule as far as possible
-# instead.
-no_stamp_files = true
-
 # These arguments override the default values for items in a declare_args
 # block. "gn args" in turn can override these.
 #