Bug 1491434 - Add apphelp.dll to talos xperf whitelist. r=jmaher

This gets accessed in beta simulations since xperf has been enabled on Windows 10.

Differential Revision: https://phabricator.services.mozilla.com/D8516

--HG--
extra : moz-landing-system : lando

testing/talos/talos/xtalos/xperf_whitelist.json

@@ -74,6 +74,12 @@
   "c:\\windows\\prefetch\\{prefetch}.pf": {
     "ignore": true
   },
+  "c:\\windows\\system32\\apphelp.dll": {
+    "mincount": 0,
+    "maxcount": 2,
+    "minbytes": 0,
+    "maxbytes": 32768
+  },
   "c:\\windows\\system32\\windows.storage.dll": {
     "mincount": 2,
     "maxcount": 2,