Remove failing test that works with mocks only anyway

[nickvergessen]

Since PHPUnit 9.5 this test fails. However the function is so plain:

server/lib/private/Encryption/Util.php

Lines 296 to 299 in f5c361c

	public function isSystemWideMountPoint(string $path, string $uid) {
	$mount = Filesystem::getMountManager()->find('/' . $uid . $path);
	return $mount instanceof ISystemMountPoint;
	}

That testing it with mocks doesn't really make a lot of sense.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[nickvergessen]

/backport to stable25

[nickvergessen]

/backport to stable24

[nickvergessen]

backports in:

• [stable25] chore(CI): Opt-out of PHPUnit 10 for now #36518
• [stable24] chore(CI): Opt-out of PHPUnit 10 for now #36519