Add optional arg to the OptionsInput macro call to remove the optional label from the form

Disable the button to update the PPoC when there is only one portfolio
member

styles/elements/_buttons.scss

@@ -7,7 +7,6 @@
 button,
 [type="button"] {
   &:disabled {
-    background-color: unset;
     opacity: 0.75;
   }
 }

templates/portfolios/fragments/change_ppoc.html

@@ -21,7 +21,8 @@
     <div class='form-col form-col--half'>
       {{
         OptionsInput(
-          assign_ppoc_form.role_id
+          assign_ppoc_form.role_id,
+          optional=False
         )
       }}
     </div>
@@ -65,9 +66,10 @@
 {% endset %}
 
 <div class="flex-reverse-row">
-  <a class="usa-button-primary" v-on:click="openModal('change-ppoc-form')">
+  {% set disable_ppoc_button = 1 == portfolio.members |length %}
+  <button type="button" class="usa-button usa-button-primary" v-on:click="openModal('change-ppoc-form')" {% if disable_ppoc_button %}disabled{% endif %}>
     {{ "fragments.ppoc.update_btn" | translate }}
-  </a>
+  </button>
   {{
     MultiStepModalForm(
       'change-ppoc-form',