storage_file_probe: Remove unused state 'BACKING_STORE_ERROR'

None of the backing store parser functions actually use it. Remove it to
avoid confusion.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

src/storage_file/storage_file_probe.c

@@ -46,7 +46,6 @@ enum lv_endian {
 enum {
     BACKING_STORE_OK,
     BACKING_STORE_INVALID,
-    BACKING_STORE_ERROR,
 };
 
 #define FILE_TYPE_VERSIONS_LAST 3
@@ -963,9 +962,6 @@ virStorageFileProbeGetMetadata(virStorageSource *meta,
 
         if (store == BACKING_STORE_INVALID)
             return 0;
-
-        if (store == BACKING_STORE_ERROR)
-            return -1;
     }
 
     g_clear_pointer(&meta->features, virBitmapFree);