Activate is_offcial_build option for perf builders

Bug: v8:9898
Change-Id: I41e1fcb37755906e29e6937b805cfb3018e90438
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1888937Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Liviu Rau <liviurau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64640}

infra/mb/mb_config.pyl

@@ -722,8 +722,7 @@
     },
 
     'official': {
-      # TODO(liviurau): switch this to true after new perf builders are in use
-      'gn_args': 'is_official_build=false',
+      'gn_args': 'is_official_build=true',
     },
 
     'shared': {