Move passing of mavlink traffic to Follow library up to GCS_MAVLink base class

[peterbarker]

Board                    AP_Periph  blimp  bootloader  copter  heli  iofirmware  plane  rover  sub
CubeOrange-periph-heavy  *                                                                     
Durandal                            *      *           24      24                80     56     *
Hitec-Airspeed           *                                                                     
KakuteH7-bdshot                     *      *           -8      -8                88     96     *
MatekF405                           0      *           0       0                 0      -1440  0
Pixhawk1-1M-bdshot                  0                  0       0                 0      -1368  0
f103-QiotekPeriph        *                                                                     
f303-Universal           *                                                                     
iomcu                                                                *                         
revo-mini                           0      *           0       0                 0      -1496  0
skyviper-v2450                                         -80                                     

actually fixes a bug in Rover where we may try to use the singleton when it isn't instantiated.

... now actually just removes from the smaller boards. The methods being crossed in Rover may have been method-on-nullptr traps.

[tridge]

looks good, but need to check ship landing with lua on quadplane