strip comments from quad x mixer file because else it fails to load on Snapdragon

ROMFS/px4fmu_common/mixers/quad_x.main.mix

-Multirotor mixer for PX4FMU
-===========================
-
-This file defines a single mixer for a quadrotor in the X configuration.  All controls
-are mixed 100%.
-
 R: 4x 10000 10000 10000 0
-
-Gimbal / payload mixer for last four channels
------------------------------------------------------
-
 M: 1
 O:      10000  10000      0 -10000  10000
 S: 0 4  10000  10000      0 -10000  10000
-
 M: 1
 O:      10000  10000      0 -10000  10000
 S: 0 5  10000  10000      0 -10000  10000
-
 M: 1
 O:      10000  10000      0 -10000  10000
 S: 0 6  10000  10000      0 -10000  10000
-
 M: 1
 O:      10000  10000      0 -10000  10000
 S: 0 7  10000  10000      0 -10000  10000