Remove dead telemetryTimePointToSecondsSinceEpoch helper

Summary:
`telemetryTimePointToSecondsSinceEpoch()` in `ReactCommon/react/utils/Telemetry.h` was a `static inline` helper that converted a `TelemetryTimePoint` to seconds since the UNIX epoch, but it had no callers anywhere. This is a pure dead-code removal. The sibling `clockCast` helper it used is left in place (it remains part of the public API surface).

Changelog: [Internal]

Differential Revision: D108012910

Author: sammy-SC

packages/react-native/ReactCommon/react/utils/Telemetry.h

@@ -81,19 +81,6 @@ DestinationTimePointT clockCast(SourceTimePointT timePoint)
       timePoint - sourseClockNow + destinationClockNow);
 }
 
-/*
- * Returns a number of seconds that passed from the UNIX Epoch starting time
- * point to a given time point.
- * Also known as POSIX time or UNIX Timestamp.
- */
-static inline double telemetryTimePointToSecondsSinceEpoch(TelemetryTimePoint timePoint)
-{
-  auto systemClockTimePoint = clockCast<std::chrono::system_clock::time_point, TelemetryTimePoint>(timePoint);
-  return (double)std::chrono::duration_cast<std::chrono::microseconds>(systemClockTimePoint.time_since_epoch())
-             .count() /
-      1000000.0;
-}
-
 /*
  * Returns a number of milliseconds that represents the given duration object.
  */