Switch Win10 Intel Exp builder to single pool

Switches the win10_intel_hd_630_experimental mixin to trigger tests only
in chromium.tests.gpu.experimental.template, as apparently the OR
operator is explicitly not supported for pools for security reasons.

TBR=ynovikov@chromium.org

No-try: true
Bug: 1065505, 1053803
Change-Id: I846d13d0f402c9ba7d98ebc0b2d8fbb826510a2b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2154499
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Brian Sheedy <bsheedy@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#760587}

testing/buildbot/mixins.pyl

@@ -694,7 +694,7 @@
       'dimensions': {
         'gpu': '8086:5912-26.20.100.7870',
         'os': 'Windows-10',
-        'pool': 'chromium.tests.gpu.template|chromium.tests.gpu.experimental.template',
+        'pool': 'chromium.tests.gpu.experimental.template',
       },
     },
   },