registration: Don't remove LDAP populated full name.

This commit fixes a bug that caused:
1: A valid full name on an onboarding form to be cleared after an
invalid submission.
2: Incorrectly cleared name populated from LDAP which was janky from
UX perspective.

Ideally we should disable name change for LDAP as next login
will overwrite any changes but I think that can be done in a
separate PR.

Fixes: #10867.

static/js/portico/signup.js

@@ -146,7 +146,6 @@ $(function () {
         } else {
             $("#full_name_input_section").show();
             $("#profile_info_section").hide();
-            $("#id_full_name").val("");
         }
     }