LibDSP: Remove unused Effects::Delay::m_old_delay_size member

SonarCloud flagged this as m_delay_buffer is technically uninitialized
at the point at which the POD types are initialized in a constructor.

I don't check to see if this was actually a real issue, as the member
is ultimately unused. So lets just get rid of it.

Userland/Libraries/LibDSP/Effects.cpp

@@ -29,7 +29,6 @@ void Delay::handle_delay_time_change()
     if (sample_count != m_delay_buffer.size()) {
         m_delay_buffer.resize(sample_count, true);
         m_delay_index %= max(m_delay_buffer.size(), 1);
-        m_old_delay_size = m_delay_buffer.size();
     }
 }
 

Userland/Libraries/LibDSP/Effects.h

@@ -29,7 +29,6 @@ private:
 
     Vector<Sample> m_delay_buffer;
     size_t m_delay_index { 0 };
-    size_t m_old_delay_size = m_delay_buffer.size();
 };
 
 // A simple effect that applies volume, mute and pan to its input signal.