Use master branch of aosp for expat:

Inlcudes some libstdc++ fixes for newer toolchains such as this: https://github.com/android/platform_external_expat/commit/af67dda3fccc957a74b29dc2ba8e709b08e3dd7d
Merge branch 'kitkat-legacy' of https://github.com/AOSPAL/manifest into kitkat-legacy