util: fix clang-tidy modernize-use-equals-default error

mp/include/mp/util.h:173:5: error: use '= default' to define a trivial destructor [modernize-use-equals-default,-warnings-as-errors]
  173 |     ~Lock() MP_RELEASE() {}
      |     ^                    ~~
      |                          = default;

Author: ryanofsky

include/mp/util.h

@@ -174,7 +174,7 @@ class MP_CAPABILITY("mutex") Mutex {
 class MP_SCOPED_CAPABILITY Lock {
 public:
     explicit Lock(Mutex& m) MP_ACQUIRE(m) : m_lock(m.m_mutex) {}
-    ~Lock() MP_RELEASE() {}
+    ~Lock() MP_RELEASE() = default;
     void unlock() MP_RELEASE() { m_lock.unlock(); }
     void lock() MP_ACQUIRE() { m_lock.lock(); }
     void assert_locked(Mutex& mutex) MP_ASSERT_CAPABILITY() MP_ASSERT_CAPABILITY(mutex)