Remove old local-only linux debugging code

Summary:
Currently, the local-only path fails about 50% of the tests, which means that: a) nobody is using
it; and b) the remote debugging path is much more stable. This commit removes the local-only
linux debugging code (ProcessLinux) and makes remote-loopback the only way to debug local
applications (the same architecture as OSX). The ProcessPOSIX code is moved to the FreeBSD
directory, which is now the only user of this class. Hopefully, FreeBSD will soon move to the new
architecture as well and then this code can be removed completely.

Test Plan: Test suite passes via remote stub.

Reviewers: emaste, vharron, ovyalov, clayborg

Subscribers: tberghammer, emaste, lldb-commits

Differential Revision: http://reviews.llvm.org/D10661

llvm-svn: 240543