[libcxxabi] NFC: fix incorrect indentation of braces

Some functions in cxa_exception_storage.cpp have incorrect indentation
of braces; fix them.
Original patch by Zhouyi Zhou <zhouzhouyi@gmail.com>

Also, remove a line of commented-out (and no-longer-possible-to-compile)
code. That thread-safe-static initialization of `init` was replaced
with the call to pthread_once directly above it, back in 2012.

Differential Revision: https://reviews.llvm.org/D109408