[tools] Remove support for v8_nexus9_perf_try

TBR=machenbach@chromium.org

No-Try: true
Bug: chromium:838864
Change-Id: Id4881bd0cd01564cb969da7aad855a7ce6685bb8
Reviewed-on: https://chromium-review.googlesource.com/1168482
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54993}

tools/try_perf.py

@@ -16,7 +16,6 @@ BOTS = {
   '--linux64_haswell': 'v8_linux64_haswell_perf_try',
   '--nexus5': 'v8_nexus5_perf_try',
   '--nexus7': 'v8_nexus7_perf_try',
-  '--nexus9': 'v8_nexus9_perf_try',
   '--nexus10': 'v8_nexus10_perf_try',
   '--pixel2': 'v8_pixel2_perf_try',
 }