Revert "Fix bug with namespace undeclaration"

This reverts commit 4def0fc.

lang/spec.html

@@ -1051,6 +1051,9 @@ <h5>XML namespaces</h5>
 that declares a prefix with that namespace and it is not redeclared by the
 [namespace attributes], then that prefix is used. Otherwise generate a prefix
 and add an AII to the [namespace attributes] to declare it.</li>
+<li>If the EII has no [namespace name] property, but a default namespace
+declaration is in scope, then an <code>xmlns=""</code> AII is added to the
+[namespace attributes] property to undeclare the default namespace.</li>
 <li>If the EII has a [namespace name] property N, then we need
 to ensure that there is an applicable namespace declaration:
 <ol>
@@ -1063,8 +1066,8 @@ <h5>XML namespaces</h5>
 already declared as N; if there is one, set the [prefix] property of the EII to
 P;</li>
 <li>otherwise, if the [namespace attributes] property does not contain a default
-namespace declaration or undeclaration, generate a default namespace declaration
-for N and add it to the [namespace attributes] property;</li>
+namespace declaration, generate a default namespace declaration for N and add it
+to the [namespace attributes] property;</li>
 <li>otherwise, generate a new prefix P, set the [prefix] property of the EII to
 P, and add an AII to the [namespace attributes] to declare it.</li>
 </ol>