Add NHS number code instead of dummy NHS number

Author: sarawilcox

app/views/content/writing-nhs-messages.njk

@@ -408,7 +408,7 @@
   classes: "nhsuk-expander"
 }) %}
 <p><strong>Reference number -</strong></p>
-<p><strong>NHS number -</strong> 999 123 4567</p>
+<p><strong>NHS number -</strong> ((NHS number))</p>
 <p>Dear ((firstName))((lastName)),</p>
 <p><strong>Confirm your address with NHS England</strong></p>
 <p>We are writing to you to confirm if the home address the NHS holds for you is up to date.</p>
@@ -445,7 +445,7 @@
   classes: "nhsuk-expander"
 }) %}
 <p>Date: DD MONTH YYYY</p>
-<p>Your NHS number: 999 123 4567</p>
+<p>Your NHS number: ((NHS number))</p>
 <p><strong>Booking your measles, mumps and rubella vaccination</strong></p>
 <p>Dear ((firstName))((lastName)),</p>
 <p>Measles cases are increasing in England, so it's important you are fully vaccinated.</p>