Fix field deletion in Symbol Fields Table not updating grid

When deleting a field in the Symbol Fields Table, the underlying data
model column was removed but the grid was never notified of the change.
This caused the grid to have a stale view with more columns than the
data model actually had, resulting in field corruption where the next
field would appear to "merge" and become uneditable.

Added wxGRIDTABLE_NOTIFY_COLS_DELETED notification in RemoveColumn() to
properly sync the grid state after column removal.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/22406

eeschema/fields_data_model.cpp

@@ -265,6 +265,12 @@ void FIELDS_EDITOR_GRID_DATA_MODEL::RemoveColumn( int aCol )
     }
 
     m_cols.erase( m_cols.begin() + aCol );
+
+    if( wxGrid* grid = GetView() )
+    {
+        wxGridTableMessage msg( this, wxGRIDTABLE_NOTIFY_COLS_DELETED, aCol, 1 );
+        grid->ProcessTableMessage( msg );
+    }
 }