platforms: remove TODO
platforms: remove TODO

It turns out Mac OS X v10.11.6 (El Capitan) is still covered by security
updates at this time, so not end-of-lifed, so we might as well keep
these legacy things.

mje-nz/PX4-Firmware,dagar/Firmware,dagar/Firmware,dagar/Firmware,krbeverx/Firmware,krbeverx/Firmware,krbeverx/Firmware,acfloria/Firmware,PX4/Firmware,PX4/Firmware,acfloria/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,acfloria/Firmware,dagar/Firmware,PX4/Firmware,dagar/Firmware,acfloria/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,dagar/Firmware,PX4/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,PX4/Firmware,acfloria/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware