Remove thread safety from libbase logging / liblog

There are no libbase users that require thread safety for SetLogger,
SetAborter, or SetDefaultTag  and the equivalent liblog symbols are
unreleased, thus have effectively no users.

It is hard to imagine a scenario where a user would need to use these
functions in a multi-threaded program, and it is unreasonable for all
users to pay for thread safety for a vast minority of potential
scenarios. Thread safety implies less efficiency and necessarily means
that these functions are neither fork safe nor async-signal safe, and
we do have users who depend on those characteristics.

It is always possible for users of the non-thread safe versions of
these functions to build thread safe versions on top of them.  For
example, if a user needs a thread safe SetLogger(), they can use the
non-thread safe SetLogger at the start of their program to register a
logger that has its own lock and pointer to a logger function.

Bug: 119867234
Test: logging unit tests
Change-Id: I8afffec1a6957d3bda95502a4c59493e0c5049ce