Revert "MB-57400: "estimated" items_remaining drops to 0 when cursor settles"

This reverts commit e903cfe.

- Reason for revert -
After the backport of MB-52276 to Neo "estimate" is no longer needed.
This is the first of 2 reverts for MB-57400.

Note: Most of the code in the original patch was already removed as
part of the MB-52276 backport, so this revert ends up in a 1-liner.

Change-Id: I977af27f0831d98af810533c25d80395196465a3
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/194196
Well-Formed: Restriction Checker
Reviewed-by: Dave Rigby <[email protected]>
Tested-by: Paolo Cocchi <[email protected]>

Author: paolococchi

engines/ep/src/checkpoint_iterator.h

@@ -146,12 +146,12 @@ class CheckpointIterator {
         return iter;
     }
 
+private:
     /// Is the iterator currently pointing to the "end" element.
     bool isAtEnd() const {
         return (iter == container.get().end());
     }
 
-private:
     /// Is the iterator currently pointing to the first element,
     bool isAtStart() const {
         return (iter == container.get().begin());