Remove ENABLE/ENABLED from Plane

[peterbarker]

These were being used incorrectly in various places.

Compiler output is indentical apart from the hwdef inclusion

[peterbarker]

No copmpiler output changes whem hwdef omitted

pbarker@threads:~/rc/ardupilot$ ~/rc/ardupilot/Tools/scripts/filter_size_compare_branches_csv.py /tmp/some.csv  --hide-bin
------------------------  -----  ------  ----  -----  -----  ---
Board                     blimp  copter  heli  plane  rover  sub
SITL_arm_linux_gnueabihf  0      0       0     0      0      0
SITL_x86_64_linux_gnu     0      0       0     0      0      0
------------------------  -----  ------  ----  -----  -----  ---
pbarker@threads:~/rc/ardupilot$