Get rid of Error::PutToLog().

Instead just rely on LLDB_LOG().

This is part of an effort to sort out dependency hell in LLDB.
Error is in Utility, but Log is in Core.  Core can depend on
Utility, but not vice versa.  So this patch moves the knowledge
about how to log Errors from the Error class to the Log file.

Differential Revision: https://reviews.llvm.org/D29514

llvm-svn: 294210