gh-110850: Rename internal PyTime C API functions (#115734)

Rename functions:

* _PyTime_GetSystemClock() => _PyTime_TimeUnchecked()
* _PyTime_GetPerfCounter() => _PyTime_PerfCounterUnchecked()
* _PyTime_GetMonotonicClock() => _PyTime_MonotonicUnchecked()
* _PyTime_GetSystemClockWithInfo() => _PyTime_TimeWithInfo()
* _PyTime_GetMonotonicClockWithInfo() => _PyTime_MonotonicWithInfo()
* _PyTime_GetMonotonicClockWithInfo() => _PyTime_MonotonicWithInfo()

Changes:

* Remove "typedef PyTime_t PyTime_t;" which was
  "typedef PyTime_t _PyTime_t;" before a previous rename.
* Update comments of "Unchecked" functions.
* Remove invalid PyTime_Time() comment.