all: fix typos in comments

Fix its/it's, who's/whose, wether/whether, missing apostrophes
in contractions, and other misspellings across the codebase.

Updates #cleanup

Change-Id: I20453b81a7aceaa14ea2a551abba08a2e7f0a1d8
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

tka/tailchonk.go

@@ -715,7 +715,7 @@ func markActiveChain(storage Chonk, verdict map[AUMHash]retainState, minChain in
 
 		parent, hasParent := next.Parent()
 		if !hasParent {
-			// Genesis AUM (beginning of time). The chain isnt long enough to need truncating.
+			// Genesis AUM (beginning of time). The chain isn't long enough to need truncating.
 			return h, nil
 		}