[lldb][NFC] Remove strange bool parameter from Searcher::SearchCallback

Summary:
The SearchCallback has a bool parameter that we always set to false, we never use in any callback implementation and that also changes its name
from one file to the other (either `containing` and `complete`). It was added in the original LLDB check in, so there isn't any history what
this was supposed to be, so let's just remove it.

Reviewers: jingham, JDevlieghere, labath

Reviewed By: jingham, labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68696

llvm-svn: 374313