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/shell/view/CLAUDE.md

@@ -375,15 +375,6 @@ applies the resulting lane state to live tracks.
   point — and, since the terminator above, whatever the drain had NOT yet written when
   the undo arrived, because the span closes at that instant. Whether that reads as
   correct in the DAW is `[verify — DAW]`, `docs/VERIFICATION.md` §"Mode switching".
-- **The trace of the failing mid-hold Ctrl-Z showed NO `BeginLoadProjectState` line at
-  all**, which the state-load terminator says should fire for an undo
-  (`reaper_plugin.h:1203-1205`), and the dump had not wrapped. Unexplained: either REAPER
-  declined the undo outright while our block was open, or it performed one without a state
-  load. The dispatch interception does not rest on which — it mints the point before REAPER
-  is asked, either way — but the next dump discriminates, and the expected order is
-  `[UndoIntercept]`, `[UndoSpan] CLOSE reason=undo action`, then `[Load]
-  BeginLoadProjectState isUndo=1`. A dump still missing the load line means the diagnosis
-  needs revisiting, not that the fix regressed.
 - **A NATIVE REAPER action fired during the span is absorbed into the switch's point.**
   The nesting rule and `UndoBlock` cover every EXTENSION-owned block; REAPER's own actions
   cannot be routed through it, so under the depth-counter reading their block closes at