Update README.md

Remove Community CI bots which have been offline for over 6 months.

Author: compnerd

README.md

@@ -14,9 +14,6 @@
 
 | **OS** | **Architecture** | **Build** |
 |---|:---:|:---:|
-|**[Debian 9.1 (Raspberry Pi)](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/armv7_debian_stretch.json)** | ARMv7 | [![Build Status](https://ci-external.swift.org/job/oss-swift-RA-linux-debian-9_1/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-linux-debian-9_1)|
-|**[Fedora 27](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_fedora_27.json)** | x86_64 |[![Build Status](https://ci-external.swift.org/job/oss-swift-RA-linux-fedora-27/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-linux-fedora-27)|
-|**[Ubuntu 16.04](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_ubuntu_16_04.json)** | x86_64 |[![Build Status](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04)|
 |**[Ubuntu 16.04 ](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/ppc64le_ubuntu_16_04.json)** | PPC64LE |[![Build Status](https://ci-external.swift.org/job/oss-swift-5.1-RA-linux-ubuntu-16.04-ppc64le/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-5.1-RA-linux-ubuntu-16.04-ppc64le)|
 |**[Ubuntu 16.04 ](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/aarch64_ubuntu_16.04.json)** | AArch64 |[![Build Status](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04-aarch64/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04-aarch64)|
 |**[Android](https://github.com/apple/swift-community-hosted-continuous-integration/blob/master/nodes/x86_64_ubuntu_16_04_LTS_android.json)** | ARMv7 |[![Build Status](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04-android/lastCompletedBuild/badge/icon)](https://ci-external.swift.org/job/oss-swift-RA-linux-ubuntu-16.04-android)|