refactor: Remove unused GetTimeMillis

The function is unused, not type-safe, and does not denote the
underlying clock type. So remove it.

src/util/time.cpp

@@ -78,14 +78,6 @@ NodeClock::time_point NodeClock::now() noexcept
     return time_point{ret};
 };
 
-template <typename T>
-static T GetSystemTime()
-{
-    const auto now = std::chrono::duration_cast<T>(std::chrono::system_clock::now().time_since_epoch());
-    assert(now.count() > 0);
-    return now;
-}
-
 void SetMockTime(int64_t nMockTimeIn)
 {
     Assert(nMockTimeIn >= 0);
@@ -102,11 +94,6 @@ std::chrono::seconds GetMockTime()
     return std::chrono::seconds(nMockTime.load(std::memory_order_relaxed));
 }
 
-int64_t GetTimeMillis()
-{
-    return int64_t{GetSystemTime<std::chrono::milliseconds>().count()};
-}
-
 int64_t GetTime() { return GetTime<std::chrono::seconds>().count(); }
 
 std::string FormatISO8601DateTime(int64_t nTime) {

src/util/time.h

@@ -71,9 +71,6 @@ using MillisecondsDouble = std::chrono::duration<double, std::chrono::millisecon
  */
 int64_t GetTime();
 
-/** Returns the system time (not mockable) */
-int64_t GetTimeMillis();
-
 /**
  * DEPRECATED
  * Use SetMockTime with chrono type