Disable *.Arm32.Open in PullRequest and remove two queues from schedu…

…led builds (#23677)

eng/platform-matrix.yml

@@ -32,16 +32,10 @@ jobs:
         osIdentifier: Linux
         containerName: ubuntu_1404_arm_cross_build_image
         helixQueues:
-        # The following is to balance the load on Linux/arm32 hardware between two different sets of machines (Ubuntu.1404.Arm32.Open and Ubuntu.1604.Arm32.Open).
-        # This should make situations when a queue is overflowed with work items coming from different sources (PRs, CI and scheduled builds) less frequent.
-        - ${{ if and(eq(variables['System.TeamProject'], 'public'), eq(variables['Build.Reason'], 'PullRequest')) }}:
-          - (Ubuntu.1804.Arm32.Open)Ubuntu.1604.Arm32.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-helix-arm32v7-0a0ebdd-20190312215532
         # Ubuntu.1404.Arm32.Open is used only by CI while Ubuntu.1604.Arm32.Open serves PRs and scheduled builds.
         - ${{ if and(eq(variables['System.TeamProject'], 'public'), in(variables['Build.Reason'], 'IndividualCI', 'BatchedCI')) }}:
           - Ubuntu.1404.Arm32.Open
         - ${{ if and(eq(variables['System.TeamProject'], 'public'), notIn(variables['Build.Reason'], 'PullRequest', 'IndividualCI', 'BatchedCI')) }}:
-          - (Debian.9.Arm32.Open)Ubuntu.1604.Arm32.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:debian-9-helix-arm32v7-0a0ebdd-20190312215452
-          - (Ubuntu.1604.Arm32.Open)Ubuntu.1604.Arm32.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-16.04-helix-arm32v7-0a0ebdd-20190312215551
           - (Ubuntu.1804.Arm32.Open)Ubuntu.1604.Arm32.Open@mcr.microsoft.com/dotnet-buildtools/prereqs:ubuntu-18.04-helix-arm32v7-0a0ebdd-20190312215532
         - ${{ if eq(variables['System.TeamProject'], 'internal') }}:
           - (Debian.9.Arm32)Ubuntu.1604.Arm32@mcr.microsoft.com/dotnet-buildtools/prereqs:debian-9-helix-arm32v7-0a0ebdd-20190312215452