storage: remove allocs from iter.Close

I actually don't understand why this allocated.
Escape analysis said:

> func literal escapes to heap: flow: {heap} =
> &{storage for func literal}: from func literal (spill) at <the defer>

This remained true even after simplifying the code (so that `iter, err`
were local to the block) but keeping the `defer`.

This was 0.41% on oltp_write_only.

pkg/storage/mvcc.go

@@ -5241,19 +5241,16 @@ func MVCCResolveWriteIntent(
 		if str == lock.Intent {
 			// Intent resolution requires an MVCC iterator to look up the MVCC
 			// version associated with the intent. Create one.
-			var iter MVCCIterator
-			{
-				iter, err = rw.NewMVCCIterator(ctx, MVCCKeyIterKind, IterOptions{
-					Prefix:       true,
-					KeyTypes:     IterKeyTypePointsAndRanges,
-					ReadCategory: fs.IntentResolutionReadCategory,
-				})
-				if err != nil {
-					return false, 0, nil, false, err
-				}
-				defer iter.Close()
+			iter, err := rw.NewMVCCIterator(ctx, MVCCKeyIterKind, IterOptions{
+				Prefix:       true,
+				KeyTypes:     IterKeyTypePointsAndRanges,
+				ReadCategory: fs.IntentResolutionReadCategory,
+			})
+			if err != nil {
+				return false, 0, nil, false, err
 			}
 			outcome, err = mvccResolveWriteIntent(ctx, rw, iter, ms, update, &buf.meta, buf)
+			iter.Close()
 		} else {
 			outcome, err = mvccReleaseLockInternal(ctx, rw, ms, update, str, &buf.meta, buf)
 			replLocksReleased = replLocksReleased || outcome != lockNoop