Drop dependency on rustls-pemfile #772

Job	Run time
Check for documentation errors	26s
Format	5s
Check semver compatibility	1m 14s
msrv	1m 4s
Clippy	1m 2s
features	1m 39s
Build+test (nightly, ubuntu-latest)	3m 4s
Build+test (macos-latest, stable)	2m 41s
Build+test (windows-latest, stable)	6m 16s
Build+test (stable, ubuntu-latest)	2m 55s
Build+test (beta, ubuntu-latest)	3m 13s
	23m 39s

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