Editorial: Present never-invoked concrete methods more consistently.

Specifically, present DeleteBinding for module ER
more like CreateImmutableBinding for object ER.

- Don't say it "refuses to delete bindings",
  because that sounds like it throws an error if invoked,
  when in fact it's never invoked.

- Drop the emu-alg that just asserts it's never invoked.

spec.html

@@ -6756,10 +6756,7 @@ <h1>GetBindingValue ( _N_, _S_ )</h1>
 
         <emu-clause id="sec-module-environment-records-deletebinding-n">
           <h1>DeleteBinding ( _N_ )</h1>
-          <p>The concrete Environment Record method DeleteBinding for module Environment Records refuses to delete bindings.</p>
-          <emu-alg>
-            1. Assert: This method is never invoked. See <emu-xref href="#sec-delete-operator-static-semantics-early-errors"></emu-xref>.
-          </emu-alg>
+          <p>The concrete Environment Record method DeleteBinding for module Environment Records is never used within this specification.</p>
           <emu-note>
             <p>Module Environment Records are only used within strict code and an early error rule prevents the delete operator, in strict code, from being applied to a Reference Record that would resolve to a module Environment Record binding. See <emu-xref href="#sec-delete-operator-static-semantics-early-errors"></emu-xref>.</p>
           </emu-note>