When lowering br_table to branches, delete the old jump tables.

This prevents codegen from emitting unused readonly data.

lib/codegen/src/legalizer/mod.rs

@@ -110,6 +110,11 @@ pub fn legalize_function(func: &mut ir::Function, cfg: &mut ControlFlowGraph, is
             }
         }
     }
+
+    // Now that we've lowered all br_tables, we don't need the jump tables anymore.
+    if !isa.flags().jump_tables_enabled() {
+        pos.func.jump_tables.clear();
+    }
 }
 
 // Include legalization patterns that were generated by `gen_legalizer.py` from the `XForms` in