Remove the synchronized block

As the new start() method is only called once during wiremock
initialisation we no longer need the initialised flag or the
synchronised block.

src/main/java/org/wiremock/extension/jwt/JwtHelpersExtension.java

@@ -7,7 +7,6 @@
 public class JwtHelpersExtension implements TemplateHelperProviderExtension {
 
     private final JwtSigningKeySettings jwtSigningKeySettings;
-    private boolean initialised = false;
 
     public JwtHelpersExtension(JwtSigningKeySettings jwtSigningKeySettings) {
         this.jwtSigningKeySettings = jwtSigningKeySettings;
@@ -26,20 +25,9 @@ public Map<String, Helper<?>> provideTemplateHelpers() {
 
     @Override
     public void start() {
-        initialise();
+        jwtSigningKeySettings.initialise();
     }
 
-    private void initialise() {
-        if (!initialised) {
-            synchronized (this) {
-                if (!initialised) {
-                    jwtSigningKeySettings.initialise();
-                    initialised = true;
-                }
-            }
-        }
-    }
-
     @Override
     public String getName() {
         return "jwt-template-helpers";