Unescape HTML-escaped apostrophes in regression test artefacts

Since #2098 & #2112, apostrophes rendered via `SmartAnswer::ErbRenderer` have
not been HTML-escaped. Now that we are rendering question content via this
renderer, we need to update the regression test artefacts for question pages
accordingly.

I ran the following commands to do this:

    $ find test/artefacts/calculate-your-holiday-entitlement -name '*.html' | xargs sed -i .bak "s/'/'/g"
    $ git clean -fd test/artefacts/calculate-your-holiday-entitlement/**/*.bak

Author: floehopper

test/artefacts/calculate-your-holiday-entitlement/annualised-hours.html

@@ -37,7 +37,7 @@ <h2>
   <div class="question-body">
 
 
-      <p class="hint">This is calculated by excluding statutory entitlement. This calculation isn&#39;t suitable for term-time workers.</p>
+      <p class="hint">This is calculated by excluding statutory entitlement. This calculation isn't suitable for term-time workers.</p>
 
     <div class="">
 

test/artefacts/calculate-your-holiday-entitlement/casual-or-irregular-hours.html

@@ -37,7 +37,7 @@ <h2>
   <div class="question-body">
 
 
-      <p class="hint">The holiday entitlement may be calculated as the leave builds up (&#39;accrues&#39;) for each hour worked.</p>
+      <p class="hint">The holiday entitlement may be calculated as the leave builds up ('accrues') for each hour worked.</p>
 
     <div class="">