Revert "Partial revert of: 'Bump xcode versions for WebRTC bots.'"

This reverts commit 47c48b803202ec0132df06f20c7f16267524ab1a.

Reason for revert: Machines have been upgraded.

Original change's description:
> Partial revert of: 'Bump xcode versions for WebRTC bots.'
> 
> Partial revert of https://webrtc-review.googlesource.com/c/src/+/97060.
> These machines need to be updated to a newer OS version.
> 
> Bug: None
> Change-Id: Ice30ff9125eb366a6d6f93080ae7d0bceba1fe8b
> Reviewed-on: https://webrtc-review.googlesource.com/98400
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#24603}

TBR=phoglund@webrtc.org,mbonadei@webrtc.org,oprypin@webrtc.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: None
Change-Id: I7de961d6b6d3b472b0e6bbae545c1902e9a4d0c3
Reviewed-on: https://webrtc-review.googlesource.com/99223
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Oleh Prypin <oprypin@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24663}

tools_webrtc/ios/internal.client.webrtc/iOS64_Debug.json

@@ -2,7 +2,7 @@
   "comments": [
     "Tests for 64-bit iOS devices."
   ],
-  "xcode build version": "9C40b",
+  "xcode build version": "10l232m",
   "gn_args": [
     "goma_dir=\"$(goma_dir)\"",
     "is_component_build=false",

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

@@ -2,7 +2,7 @@
   "comments": [
     "Tests for 64-bit iOS devices."
   ],
-  "xcode build version": "9C40b",
+  "xcode build version": "10l232m",
   "gn_args": [
     "goma_dir=\"$(goma_dir)\"",
     "is_component_build=false",

tools_webrtc/ios/internal.client.webrtc/iOS64_Release.json

@@ -2,7 +2,7 @@
   "comments": [
     "Tests for 64-bit iOS devices."
   ],
-  "xcode build version": "9C40b",
+  "xcode build version": "10l232m",
   "gn_args": [
     "dcheck_always_on=true",
     "goma_dir=\"$(goma_dir)\"",