Remove external/bison

This is now built in the build-tools branch on AOSP, and submitted to
the platform tree as prebuilts under prebuilts/build-tools. There's no
need for the source to exist in the platform tree anymore.

Test: m
Change-Id: Icbd169b34c51348a6ceb8b083405e9243ba13c89
Merged-In: Icbd169b34c51348a6ceb8b083405e9243ba13c89
1 file changed
tree: 540485f4b6ec0239bad949e836efe0f4e0b05414
  2. default.xml