Revert "mac: Update LSMinimumSystemVersion from 10.10 to 10.11"

This reverts commit 4f35dbaf.

Reason for revert: Suspect causing chromedriver_py_tests failures on (none) GPU on Mac:
- main.MobileEmulationCapabilityTest.testNetworkConnectionDisabledByDefault
- main.ChromeDriverTestLegacy.testMobileEmulationDisabledByDefault
- main.ChromeDriverTest.testActionsMouseDrag
- main.ChromeDriverTestLegacy.testMouseDoubleClick
...215 more failure(s) (219 total)...

First build failure: https://ci.chromium.org/p/chromium/builders/ci/Mac10.10%20Tests/61407

Sample log:
---
testWifiAndAirplaneModeEmulation (__main__.MobileEmulationCapabilityTest) ... ERROR
testConnectToRemoteBrowser (__main__.RemoteBrowserTest) ... application requires at least Mac OS X version 10.11.0 (10.11.0), but is being run on 10.10.5 ( 10.10.5/14F2511), and so is exiting.Received signal 6
---

Original change's description:
> mac: Update LSMinimumSystemVersion from 10.10 to 10.11
>
> Bug: 1148931
> Change-Id: Ic0cdded0c1c4821689486cacd5790fce82c40c87
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2537057
> Reviewed-by: Avi Drissman <avi@chromium.org>
> Commit-Queue: Robert Sesek <rsesek@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#827937}

TBR=avi@chromium.org,rsesek@chromium.org

Change-Id: If527cdb6ffdde2807b2c9a2315316a8ae5699e24
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1148931
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2542934Reviewed-by: Takashi Sakamoto <tasak@google.com>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828010}

build/config/mac/mac_sdk.gni

@@ -24,7 +24,7 @@ declare_args() {
   # dropping support for older macOSes. This should be greater than or equal to
   # the mac_deployment_target version.
   # Must be of the form x.x.x for Info.plist files.
-  mac_min_system_version = "10.11.0"
+  mac_min_system_version = "10.10.0"
 
   # Path to a specific version of the Mac SDK, not including a slash at the end.
   # If empty, the path to the lowest version greater than or equal to