Remove include/backtrace symlink.

This requires a few other changes to support building libutils
properly. It does appear the windows versions of libutils is
referencing CallStack code, but it doesn't seem to cause any problems.
However, I removed those references completely for the windows build.

Also removed a few extra spaces that seem to have accumulated in the
RefBase.cpp.

Bug: 170465278

Test: Builds and libutils unit tests pass.
Change-Id: Ibeee7791b13636b34bdd592c5420fd91620f752a