ci: Update certain Android branches for recent upstream changes

[nathanchance]

android-4.19 has been moved to deprecated/android-4.19, meaning it will no longer see updates. android-4.19-stable should be the equivalent (similar to android-4.14-stable):

https://android-review.googlesource.com/c/kernel/manifest/+/1359844

Fixes the following builds:

https://travis-ci.com/github/ClangBuiltLinux/continuous-integration/jobs/359204121 https://travis-ci.com/github/ClangBuiltLinux/continuous-integration/jobs/359204126

Additionally, android-5.4 has been shuffled to android12-5.4:

https://android-review.googlesource.com/c/kernel/manifest/+/1358083 https://android-review.googlesource.com/c/kernel/manifest/+/1358088

android-5.4 still technically exists but do not rely on that always being true and just do that change now so that we do not have to do it later when the build breaks.

Presubmit: https://travis-ci.com/github/nathanchance/continuous-integration/builds/175084826

[nickdesaulniers]

thanks! 🎆 I had some heads up about this this week, but not on when the final decision was made.