Fix webrtc-internal configs to run perf tests on separate bots

Test execution was broken by specifying pool.
No need to do it once we specify bot ids in included json configs.

Bug: webrtc:10047
Change-Id: Ica5b891b796eec69573cc39d1d72617a68169499
Reviewed-on: https://webrtc-review.googlesource.com/c/112129
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Commit-Queue: Artem Titarenko <artit@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25804}

tools_webrtc/ios/internal.client.webrtc/iOS64_Perf.json

@@ -23,12 +23,6 @@
       "include": "perf_tests.json",
       "device type": "iPhone 7",
       "os": "11.4.1",
-      "dimensions": [
-        {
-          "os": "Mac",
-          "pool": "Chrome"
-        }
-      ]
     }
   ]
 }

tools_webrtc/ios/internal.tryserver.webrtc/ios_arm64_perf.json

@@ -23,12 +23,6 @@
       "include": "perf_trybot_tests.json",
       "device type": "iPhone 7",
       "os": "11.0.3",
-      "dimensions": [
-        {
-          "os": "Mac",
-          "pool": "Chrome"
-        }
-      ]
     }
   ]
 }