unit: drop ProtectClock=yes from systemd-udevd.service

unit: drop ProtectClock=yes from systemd-udevd.service

This partially reverts cabc1c6d7adae658a2966a4b02a6faabb803e92b.

The setting ProtectClock= implies DeviceAllow=, which is not suitable
for udevd. Although we are slowly removing cgropsv1 support, but
DeviceAllow= with cgroupsv1 is necessarily racy, and reloading PID1
during the early boot process may cause issues like #24668.

Let's disable ProtectClock= for udevd. And, if necessary, let's
explicitly drop CAP_SYS_TIME and CAP_WAKE_ALARM (and possibly others)
by using CapabilityBoundingSet= later.

Fixes #24668.