WATCHLISTS: fix polymer match

remove trailing '|' in last entry; since:
e7a443f Cleanup various WebUI related paths in WATCHLISTS.

Change-Id: I20a1b670666b6f2ea858411f2b3b5d2f454f9446
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3256418
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: James Zern <jzern@google.com>
Cr-Commit-Position: refs/heads/main@{#937182}

WATCHLISTS

@@ -1570,7 +1570,7 @@
     'polymer': {
       'filepath': 'third_party/polymer/|'\
                   'third_party/web-animations-js/|'\
-                  'tools/polymer|'
+                  'tools/polymer'
     },
     'popup_blocker': {
       'filepath': 'chrome/browser/ui/blocked_content'