don't include liblog to APEXes

liblog is a platform library that provides stable C API. There is no
need to include the library, especialy by statically linking to it, in
any APEX. It not only wastes the storage/ram, but also is incorrect
because the socket interface to logd which is implemented in liblog is
not guaranteed to be stable.

Fixing this issue by converting static_libs: ["liblog"] into
shared_libs: ["liblog"], in which case the dependency to the library
is satisfied via the stub variant of the library.

As a result, we could restrict the availablity of the library to
the platform and the runtime APEX.

Exempt-From-Owner-Approval: already approved when this was in internal
master (ag/10572699)

Bug: http://b/151051671
Bug: http://b/150827719
Test: m
Merged-In: I5aab863cb12b8767b6979255c247000a59355b0e
(cherry picked from commit 95b6f45b)
Change-Id: I5aab863cb12b8767b6979255c247000a59355b0e