Drop REASON_SHARED_APK.

This reason was only used by "system shared libraries", not shared
APKs like GMS.

Code that uses this reason is now obsolete, as we do compile these shared
libraries when we see an apk that uses it.

bug:33799337
Test: m -j32 && boot
Change-Id: I2eef22797551401a5c39ed339bc2486cf0d091a8
(cherry picked from commit 86d1e9e2)