[tests] remove reference to linux-xenial-rel

Bug: 964197
Change-Id: Ifff187fc6db7824edc84b99b8693734e0cd60564
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/build/+/1617290
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Ben Pastene <bpastene@chromium.org>
diff --git a/tests/masters_recipes_test.py b/tests/masters_recipes_test.py
index 88a6568..a90d642 100755
--- a/tests/masters_recipes_test.py
+++ b/tests/masters_recipes_test.py
@@ -152,7 +152,6 @@
         'linux-gcc-rel',
         'linux-rel',
         'linux-ozone-rel',
-        'linux-xenial-rel',
         'linux_chromium_asan_rel_ng',
         'linux_chromium_cfi_rel_ng',
         'linux_chromium_compile_dbg_ng',