multiline: remove incorrect flush

we are flushing the stream buffer in case it is
different in two consecutive runs, which leads to
incorrect parsing of multiline logs where we have
messages from different streams (stderr & stdout for ex)
interleaved

Signed-off-by: Aditya Prajapati <[email protected]>

src/multiline/flb_ml.c

@@ -234,7 +234,6 @@ static int package_content(struct flb_ml_stream *mst,
     }
     else {
         if (mst->last_stream_group != stream_group) {
-            flb_ml_flush_stream_group(parser, mst, mst->last_stream_group, FLB_FALSE);
             mst->last_stream_group = stream_group;
         }
     }