Remove unnecessary null pointer checks (#6358)

As reported by @elfring, we had several points in our code where
it was unnecessary to check pointers were non-null before deleting them.

Fixes https://github.com/meshtastic/firmware/issues/6170

src/AudioThread.h

@@ -41,10 +41,8 @@ class AudioThread : public concurrency::OSThread
             delete i2sRtttl;
             i2sRtttl = nullptr;
         }
-        if (rtttlFile != nullptr) {
-            delete rtttlFile;
-            rtttlFile = nullptr;
-        }
+        delete rtttlFile;
+        rtttlFile = nullptr;
 
         setCPUFast(false);
     }