Reenable load:tools:gmail on Android

Based on a try job launched in the linked bug, this story
appears to be passing now.

TBR=nednguyen@chromium.org

Bug: 657433
Change-Id: Id2351f2dd2f763d695a1256c72f6e5aff53677b0
Reviewed-on: https://chromium-review.googlesource.com/1143446
Commit-Queue: Charlie Andrews <charliea@chromium.org>
Reviewed-by: Charlie Andrews <charliea@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577645}

tools/perf/expectations.config

@@ -246,7 +246,6 @@ crbug.com/846022 [ Linux ] system_health.common_desktop/browse:social:twitter_in
 
 # Benchmark: system_health.common_mobile
 crbug.com/865464 [ Android_Webview ] system_health.common_mobile/browse:chrome:omnibox [ Skip ]
-crbug.com/657433 [ Android ] system_health.common_mobile/load:tools:gmail [ Skip ]
 crbug.com/714650 [ Android ] system_health.common_mobile/browse:news:globo [ Skip ]
 crbug.com/865466 [ Android_Webview ] system_health.common_mobile/long_running:tools:gmail-background [ Skip ]
 crbug.com/787001 [ Android_Webview ] system_health.common_mobile/load:media:soundcloud [ Skip ]