Remove unnecessary try / catch

The code is adequately guarded against reference errors etc., so it
shouldn't error even in browsers without support for the performance
API.

If ther were an issue, we still would have had some unhandled errors,
because the addEventListener callback wouldn't be covered by the try /
catch.

Simpler just to remove it.

app/assets/javascripts/govuk_publishing_components/custom-rum-data.js

@@ -25,20 +25,16 @@
     }
   }
 
-  try {
-    if (window.performance && performance.getEntriesByType) {
-      // Because the `nextHopProtocol` isn't immediately available - it seems to need
-      // a request to be made before it's populated - we need to wait for the
-      // `DOMContentReady` event before we can see what the HTTP version is.
-      if (document.readyState === 'complete') {
+  if (window.performance && performance.getEntriesByType) {
+    // Because the `nextHopProtocol` isn't immediately available - it seems to need
+    // a request to be made before it's populated - we need to wait for the
+    // `DOMContentReady` event before we can see what the HTTP version is.
+    if (document.readyState === 'complete') {
+      measureCustomData()
+    } else {
+      window.addEventListener('load', function() {
         measureCustomData()
-      } else {
-        window.addEventListener('load', function() {
-          measureCustomData()
-        })
-      }
+      })
     }
-  } catch (e) {
-    console.error('Error in LUX reporting the HTTP protocol (%s):', window.location, e)
   }
 })()