Remove the unused EmptyReplayLogger from the amber engine #7449

Task Summary

EmptyReplayLogger is a no-op ReplayLogger that nothing in the engine ever constructs.

The live null object for log replay sits one layer up, at the manager. EmptyReplayLogManagerImpl inherits the ReplayLogManager trait's non-logging withFaultTolerant, so it never needs a logger at all:

ReplayLogManager.scala:51  -> EmptyReplayLogManagerImpl   (no-op manager, live)
ReplayLogManager.scala:109 -> new ReplayLoggerImpl()      (the only ReplayLogger built in main)
                              EmptyReplayLogger           (never instantiated)

69b7f9bc1 (#2230) added ReplayLogger, ReplayLoggerImpl, EmptyReplayLogger and ReplayLogManager in a single commit, so nothing ever moved layers — EmptyReplayLogger was unwired from the day it landed. No configuration selects a logger class by name either, so there is no path that revives it. The abstract base ReplayLogger stays — ReplayLoggerImpl extends it.

It acquired unit tests during the 2026 coverage work (#5554), which is why it currently looks live. The spec covers this class and nothing else, so it goes with it.

Pure deletion, no behaviour change: −171 lines.

Task Type

• Refactor / Cleanup