[Darjeeling] Remove USB clock and reset

[Razer6]

Darjeeling still uses a dedicated USB clock and reset in their clock/reset definitions although this clock is completely unused. Although both the clock and reset manager are ipgen'ed and the number of clocks is parametrizable, we cannot change that now as the testbenches are not yet templated. Their, the USB clock or reset is hardcoded. The following two issues are tracking that:

1. clkmgr tb.sv needs to be ipgened #25320
2. rstmgr tb.sv needs to be ipgened #25321

Once those issues are resolved, we can change the clock and reset definition of Darjeeling and remove USB from there.