Revert "search: concurrent evaluation of OR queries (#29281)"
Created by: bobheadxi
This reverts commit b640ccb91494ec35388d91b0da888d28a13f4cbf.
This PR seems to have introduced a regression: https://buildkite.com/sourcegraph/sourcegraph/builds/124834#4d780fbc-2814-456a-a0e1-c6eabf10e4b9/269-466