Get up-to-date logoBlockCount when removing block

Previously we were getting the logoBlockCount on block creation, but
this value could become out of date if more Site Logo blocks were added
afterward.

Now we count the number of blocks at the time of block removal, so that it
is guaranteed up-to-date, and we ensure that changes are only discarded
if there are no other Site Logo blocks on the page.

packages/block-library/src/site-logo/edit.js

@@ -368,12 +368,10 @@ export default function LogoEdit( {
 		siteIconId,
 		mediaItemData,
 		isRequestingMediaItem,
-		logoBlockCount,
 	} = useSelect( ( select ) => {
 		const { canUser, getEntityRecord, getEditedEntityRecord } = select(
 			coreStore
 		);
-		const { getGlobalBlockCount } = select( blockEditorStore );
 		const siteSettings = getEditedEntityRecord( 'root', 'site' );
 		const siteData = getEntityRecord( 'root', '__unstableBase' );
 		const _siteLogo = siteSettings?.site_logo;
@@ -404,10 +402,10 @@ export default function LogoEdit( {
 			},
 			isRequestingMediaItem: _isRequestingMediaItem,
 			siteIconId: _siteIconId,
-			logoBlockCount: getGlobalBlockCount( 'core/site-logo' ),
 		};
 	}, [] );
 
+	const { getGlobalBlockCount } = useSelect( blockEditorStore );
 	const { editEntityRecord } = useDispatch( coreStore );
 
 	useEffect( () => {
@@ -427,9 +425,11 @@ export default function LogoEdit( {
 				return;
 			}
 
+			const logoBlockCount = getGlobalBlockCount( 'core/site-logo' );
+
 			// Only discard unsaved changes if we are removing the last Site Logo block
 			// on the page.
-			if ( logoBlockCount === 1 ) {
+			if ( logoBlockCount === 0 ) {
 				editEntityRecord( 'root', 'site', undefined, {
 					site_logo: undefined,
 					site_icon: undefined,