Revert "AK: Add comparison operators to NonnullOwnPtr"

This reverts commit 50c88e5e3a6918f99cfcfb802d111cb22a87645c.

The intention was to add them to NonnullRefPtr, not NonnullOwnPtr. That
is also what was advertised in the PR, but not actually done in the
reverted commit.

AK/NonnullOwnPtr.h

@@ -135,12 +135,6 @@ public:
         return NonnullOwnPtr<U>(NonnullOwnPtr<U>::Adopt, static_cast<U&>(*leak_ptr()));
     }
 
-    bool operator==(NonnullOwnPtr const& other) const { return m_ptr == other.m_ptr; }
-    bool operator!=(NonnullOwnPtr const& other) const { return m_ptr != other.m_ptr; }
-
-    bool operator==(NonnullOwnPtr& other) { return m_ptr == other.m_ptr; }
-    bool operator!=(NonnullOwnPtr& other) { return m_ptr != other.m_ptr; }
-
 private:
     void clear()
     {