evolve: remove a check which is already done by rewriteutil.precheck() We have tests to check if fold is being performed on public cset. There is no changes in test files because testing that never touched the part this patch removes, and already caught in rewriteutil.precheck()

test-compat: create a compatibility branch for Mercurial 5.2 Mercurial 5.3rc have been released, so the stable branch is no longer about 5.2.