Copter: remove stale parameter conversions

[peterbarker]

this removes stale parameter conversions.

These patches are all in the Copter-4.0.0 tag, meaning that they are all for upgrading from a version prior to that to a version prior-or-equal-to Copter-4.0.0

Past this a user running a version of ArduCopter < 4.0.0 to something >= 4.7.0 will not have smooth parameter conversions

Board                    AP_Periph  blimp  bootloader  copter  heli   iofirmware  plane  rover  sub
CubeOrange-periph-heavy  *                                                                      
CubeRedPrimary                      *      *           -1720   -3072              *      *      *
Durandal                            *      *           -1872   -3488              *      *      *
Hitec-Airspeed           *                                                                      
KakuteH7-bdshot                     *      *           -1720   -3080              *      *      *
MatekF405                           *      *           -1712   -3072              *      *      *
Pixhawk1-1M-bdshot                  *                  -1704   -3072              *      *      *
bebop                               *                  -556    -5108              *      *      *
f103-QiotekPeriph        *                                                                      
f303-Universal           *                                                                      
iomcu                                                                 *                         
revo-mini                           *      *           -1712   -3072              *      *      *
skyviper-v2450                                         -1192                                    

[rmackay9]

optionally we could probably drop this RC_OPTIONS line too which is from Aug 2020

[peterbarker]

optionally we could probably drop this RC_OPTIONS line too which is from Aug 2020

Yeah, I really did consider it. But they I couldn't use the pretty straight-forward 3.6.9 -> 4.x.x argument as to why it was time for these to go away :-)

I was also a little surprised at how much of the conversion code did go away. I wonder if we're doing less of it now-adays...

[rmackay9]

LGTM but @bnsgeyer should approve as well because these are mostly trad heli changes

[peterbarker]

@rmackay9 I've fixed an error in this PR. Currently in master there's a block of code which is responsible for setting parameter defaults on the heli frame - and it's within a method called convert_pid_parameters (mostly not actually PID parameters either...).

I'd like to move that code out in a future PR - it's in the wrong place IMO. Probably move it up, called around the comment "now setup some frame-class specific defaults"