search: always set zoekt.MaxWallTime to deadline
Created by: keegancsmith
We always have a timeout in search. Previously we would only use "nice" behaviour for zoekt if the user explicitly opted in with a timeout. Now we always use the timeout.
Before this change if we timedout in zoekt we would report that no results were found.
Part of https://github.com/sourcegraph/sourcegraph/issues/13105
Co-Author: @beyang