Bug 1682863 - Revert nssSlot_IsTokenPresent to 3.58 after ongoing Fx hangs with slow PKCS11 devices. r=bbeurdouche

This patch reverts the `nssSlot_IsTokenPresent` changes made in bug 1663661
and bug 1679290, restoring the version used in NSS 3.58 and earlier. It's not an
actual `hg backout` because the comment in lib/dev/devt.h is worth keeping.
While removing the nested locking did resolve the hang for some (most?) third-party
modules, problems remain with some slower tokens after an even further relaxation
of the locking, which defeats the purpose of addressing the races in the first place.

The crash addressed by these patches was caused by the Intermediate Preloading
Healer in Firefox, which has been disabled. We clearly have insufficient test
coverage for third-party modules, and now that osclientcerts is enabled in Fx
Nightly, any problems caused by these and similar changes is unlikely to be
reported until Fx Beta, well after NSS RTM. I think the best option at this
point is to simply revert NSS.

Differential Revision: https://phabricator.services.mozilla.com/D100344

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