Remove system health story browse_accessibility:tools:gmail_compose

The benchmark was not completely removed in crrev/c/1143595.

Bug: 769809
Change-Id: I131b226b7388d97eb380943275b6b16c222d2260
Reviewed-on: https://chromium-review.googlesource.com/c/1257669Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: James Wallace-Lee <jamwalla@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597187}

tools/perf/page_sets/data/system_health_desktop.json

@@ -96,9 +96,6 @@
         "browse_accessibility:tech:codesearch:2018": {
             "DEFAULT": "system_health_desktop_063.wprgo"
         },
-        "browse_accessibility:tools:gmail_compose": {
-            "DEFAULT": "system_health_desktop_059.wprgo"
-        },
         "load:games:alphabetty": {
             "DEFAULT": "system_health_desktop_005.wprgo"
         },