Remove DropBox and EventLogger

They provide hooks for use by framework to intercept messages sent by
libcore. However, neither of these mechanisms are actually used by
libcore so they can be removed.

There is one method that is annotated with UnsupportedAppUsage but as
explained in bug 119748341 that appears to be a false positive reported
by the static analysis tool.

Bug: 119748341
Test: make checkbuild and flash
Change-Id: Ia8f31b2f221236f562982f7b491e2e00822dd7c7