test: remove isGlibc from common

The `common.isGlibc()` function is called exactly once from only
one test. There's no reason for it to be in `require('../common')`
at the current time. If it ends up needing to be used by multiple
tests, it can easily be moved into it's own common sub-module
(e.g. `require('../common/isglibc')` ... for now tho, just move
it into the one test that uses it and simplify the implementation
a bit to remove unnecessary caching.

PR-URL: https://github.com/nodejs/node/pull/22443


Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>