dev191 - kind of remove DIV_ALWAYS_SET_VOLUME

it's useless crap I put during the Defle compat days
it serves nearly no purpose nowadays

also why is it a command?

src/engine/platform/msm6258.h

@@ -75,6 +75,7 @@ class DivPlatformMSM6258: public DivDispatch {
     void muteChannel(int ch, bool mute);
     int getOutputCount();
     bool keyOffAffectsArp(int ch);
+    bool getLegacyAlwaysSetVolume();
     void notifyInsChange(int ins);
     void notifyInsDeletion(void* ins);
     void poke(unsigned int addr, unsigned short val);