[mlir][IR][NFC] Rename `notify*Removed` to `notify*Erased` (#82253)

Rename listener callback names:
* `notifyOperationRemoved` -> `notifyOperationErased`
* `notifyBlockRemoved` -> `notifyBlockErased`

The current callback names are misnomers. The callbacks are triggered
when an operation/block is erased, not when it is removed (unlinked).

E.g.:
```c++
/// Notify the listener that the specified operation is about to be erased.
/// At this point, the operation has zero uses.
///
/// Note: This notification is not triggered when unlinking an operation.
virtual void notifyOperationErased(Operation *op) {}
```

This change is in preparation of adding listener support to the dialect
conversion. The dialect conversion internally unlinks IR before erasing
it at a later point of time. There is an important difference between
"remove" and "erase". Lister callback names should be accurate to avoid
confusion.