Update to Swift 5.1

Remove swift-4.2-branch and swift-5.0-branch. Add swift-5.1-branch

Author: futurejones

nodes/aarch64_ubuntu_16.04.json

@@ -15,14 +15,9 @@
  "preset": "buildbot_linux,no_test"
  },
  {
- "display_name": "Swift - Ubuntu 16.04 Linux aarch64 (swift-4.2-branch)",
- "branch": "swift-4.2-branch",
+ "display_name": "Swift - Ubuntu 16.04 Linux aarch64 (swift-5.1-branch)",
+ "branch": "swift-5.1-branch",
  "preset": "buildbot_linux,no_test"
- },
- {
- "display_name": "Swift - Ubuntu 16.04 Linux aarch64 (swift-5.0-branch)",
- "branch": "swift-5.0-branch",
- "preset": "buildbot_linux,no_test"
- },
+ }
  ]
 }