extend/pathname/rmtree: improve comment. #27605

Job	Run time
syntax	46s
formula audit	6m 6s
tap syntax	4m 38s
cask audit	2m 35s
docker	4m 42s
test default formula (Ubuntu 22.04)	4m 31s
test default formula (Ubuntu 20.04)	5m 41s
tests (online)	8m 55s
test default formula (macOS 13 x86_64)	2m 27s
vendored gems	44s
tests (generic OS)	5m 49s
update-test (Ubuntu 22.04)	1m 4s
test default formula (macOS 14 arm64)	1m 13s
tests (Ubuntu 22.04)	6m 5s
update-test (macOS 13)	55s
tests (Ubuntu 20.04)	6m 49s
tests (macOS 13 x86_64)	7m 57s
tests (macOS 14 arm64)	4m 9s
	1h 15m 6s

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