[MachineOutliner] NFC: Comment tidying

The comment on describing the suffix tree had some pruning
stuff that was out of date in it.

Also fixed some typos.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@309365 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed