taildrop: remove breaking abstraction layers for apple (#10728)

Removes the avoidFinalRename logic and all associated code as it is no longer required by the Apple clients.
Enables resume logic to be usable for Apple clients.

Fixes tailscale/corp#14772

Signed-off-by: Rhea Ghosh <rhea@tailscale.com>

cmd/tailscaled/taildrop.go

@@ -27,7 +27,6 @@ func configureTaildrop(logf logger.Logf, lb *ipnlocal.LocalBackend) {
 		} else {
 			logf("%s Taildrop: using %v", dg, path)
 			lb.SetDirectFileRoot(path)
-			lb.SetDirectFileDoFinalRename(true)
 		}
 	}