LibIPC: Remove now-unused stream operator from IPC::Encoder

The fallible encoders are now the only option to encode values.

Userland/Libraries/LibIPC/Encoder.h

@@ -31,13 +31,6 @@ public:
     {
     }
 
-    template<typename T>
-    Encoder& operator<<(T const& value)
-    {
-        (void)encode(value);
-        return *this;
-    }
-
     template<typename T>
     ErrorOr<void> encode(T const& value);