Improve note about existing alleles in dialog

Refs #2758

root/static/ng_templates/allele_edit.html

@@ -139,7 +139,7 @@ <h4 class="modal-title">
         </div>
         <div class="curs-box-body">
           <div class="curs-allele-edit-sub-heading">
-            Note: this allele cannot be edited because it is already used in {{databaseName}}
+            Note: this is an existing {{databaseName}} allele
           </div>
           <table class="curs-definition-table">
             <tr>