make sure to mark entry as dirty when deleting binary.

lib/src/kdbx_entry.dart

@@ -229,6 +229,7 @@ class KdbxEntry extends KdbxObject {
     if (!binary.isInline) {
       file.ctx.removeBinary(binary);
     }
+    isDirty = true;
   }
 
   KdbxKey _uniqueBinaryName(String fileName) {

test/kdbx_binaries_test.dart

@@ -140,6 +140,7 @@ void main() {
         expect(file.ctx.binariesIterable, hasLength(2));
         entry.removeBinary(KdbxKey('example2.txt'));
         expect(file.ctx.binariesIterable, hasLength(1));
+        expect(file.dirtyObjects, [entry]);
         return await file.save();
       })();
       final file = await TestUtil.readKdbxFileBytes(saved);