histedit: pass multiple nodes to strip (BC)
Previously, histedit.cleanupnode pass root nodes one by one. Since
repair.strip takes multiple nodes and can handle them just fine, pass all
strip roots at once.
This is BC because the number of strip backup files may change from N to 1.
histedit: remove "should strip" debug message
The debug message was not used anywhere. Removed it to make
scmutil.cleanupnodes migration easier to reason about.