[NFC] Remove bits and pieces referring to Ubuntu 14.04 LTS (Trusty Tahr).

Ubuntu 20.04 LTS is out now; the last version to support 14.04 was Swift 5.1,
so it is ok to delete this.

Author: varungandhi-apple

README.md

@@ -151,8 +151,6 @@ with version 2 shipped with Ubuntu.
 
 **Note:** For Ubuntu 20.04, use `libpython2-dev` in place of the libpython-dev package above.
 
-Build instructions for Ubuntu 14.04 LTS can be found [here](docs/Ubuntu14.md).
-
 ### Getting Sources for Swift and Related Projects
 
 First create a directory for all of the Swift sources:

docs/Ubuntu14.md

@@ -968,19 +968,6 @@ mixin-preset=
     buildbot_linux_1510
     mixin_buildbot_linux,no_test
 
-# Ubuntu 14.04 preset for backwards compat and future customizations.
-[preset: buildbot_linux_1404]
-mixin-preset=buildbot_linux
-indexstore-db=0
-sourcekit-lsp=0
-
-# Ubuntu 14.04 preset that skips all tests except for integration testing of the
-# package.
-[preset: buildbot_linux_1404,notest]
-mixin-preset=
-    buildbot_linux_1404
-    mixin_buildbot_linux,no_test
-
 [preset: buildbot_linux,smoketest]
 mixin-preset=mixin_linux_installation
 build-subdir=buildbot_linux