union: remove assert in sort

Getting assertion in lyplg_type_sort_union().  This assertion
appears invalid as it comes up in test cases in SONiC but when
removed everything passes.

Signed-off-by: Brad House <[email protected]>

Author: bradh352

src/plugins_types/union.c

@@ -531,7 +531,6 @@ lyplg_type_sort_union(const struct ly_ctx *ctx, const struct lyd_value *val1, co
             break;
         }
     }
-    assert(rc != 0);
 
     return rc;
 }