Remove the temporary undo-span tracing now that the mid-drain Ctrl-Z fix has landed

Deletes the ring-buffer tracer and its diagnostic action; reverts the span
entry points to their pre-tracing no-parameter signatures.

src/app/CMakeLists.txt

@@ -40,7 +40,6 @@ add_library(reaper_reasampler MODULE
     ${REASAMPLER_SRC_DIR}/shell/capture/insert.cpp
     ${REASAMPLER_SRC_DIR}/shell/undo/undo_block.cpp
     ${REASAMPLER_SRC_DIR}/shell/undo/undo_intercept.cpp
-    ${REASAMPLER_SRC_DIR}/shell/undo/undo_trace.cpp
     ${REASAMPLER_SRC_DIR}/shell/view/view.cpp
     ${REASAMPLER_SRC_DIR}/shell/view/fx_reclaim.cpp
     ${REASAMPLER_SRC_DIR}/shell/view/view_lanes.cpp