destroyed: drop complex branchcache rebuilt logic The strip code used a trick to lower the cost of branchcache update after a strip. However is less necessary since we have branchcache collaboration. Invalid branchcache are likely to be cheaply rebuilt again a near subset of the repo. Moreover, this trick would need update to be relevant in the now filtered repository world. It currently update the unfiltered branchcache that few people cares about. Make it smarter on that aspect would need complexes update of the calling logic So this mechanism is: - Arguably needed, - Currently irrelevant, - Hard to update and I'm dropping it. We now update the branchcache in all case by courtesy of the read only reader. This changeset have a few expected impact on the testsuite are different cache are updated.