Don't print two errors for unknown commands.
Summary:
We always print two error messages when we hit an unknown command. As the function
`CommandInterpreter::HandleCommand` that prints the second error message unconditionally called the `CommandInterpreter::ResolveCommandImpl` before (which prints the first error message), we can just remove
that second error message.
Fixes https://bugs.llvm.org/show_bug.cgi?id=38312
Reviewers: labath
Reviewed By: labath
Subscribers: labath, lldb-commits
Differential Revision: https://reviews.llvm.org/D49831
llvm-svn: 338040