Don't close blocking dialog in backannotate

Back annotate is called from a dialog, so this will close itself but not
exit, locking the UI

(cherry picked from commit 28876bef90)

Fixes https://gitlab.com/kicad/code/kicad/issues/12255

eeschema/tools/backannotate.cpp

@@ -112,9 +112,6 @@ bool BACK_ANNOTATE::FetchNetlistFromPCB( std::string& aNetlist )
         frame->OpenProjectFiles( std::vector<wxString>( 1, fn.GetFullPath() ) );
     }
 
-    if( wxWindow* blocking_win = frame->Kiway().GetBlockingDialog() )
-        blocking_win->Close( true );
-
     m_frame->Kiway().ExpressMail( FRAME_PCB_EDITOR, MAIL_PCB_GET_NETLIST, aNetlist );
     return true;
 }