Remove MacOS helix queue for now (#13907)

Author: HaoK

eng/targets/Helix.Common.props

@@ -18,7 +18,6 @@
     <HelixAvailableTargetQueue Include="Windows.81.Amd64.Open" Platform="Windows" />
     <HelixAvailableTargetQueue Include="Windows.7.Amd64.Open" Platform="Windows" />
     <HelixAvailableTargetQueue Include="Windows.10.Amd64.EnterpriseRS3.ASPNET.Open" Platform="Windows" EnableByDefault="false" />
-    <HelixAvailableTargetQueue Include="OSX.1013.Amd64.Open" Platform="OSX" />
     <HelixAvailableTargetQueue Include="Ubuntu.1604.Amd64.Open" Platform="Linux" />
     <HelixAvailableTargetQueue Include="Ubuntu.1804.Amd64.Open" Platform="Linux" />
     <HelixAvailableTargetQueue Include="Centos.7.Amd64.Open" Platform="Linux" />