AP_AHRS: revert AP_Math class change

libraries/AP_AHRS/AP_AHRS_DCM.cpp

@@ -278,7 +278,7 @@ AP_AHRS_DCM::yaw_error_compass(void)
     }
 
     // update vector holding earths magnetic field (if required)
-    if( !AP_Math::is_equal(_last_declination,_compass->get_declination()) ) {
+    if( !is_equal(_last_declination,_compass->get_declination()) ) {
         _last_declination = _compass->get_declination();
         _mag_earth.x = cosf(_last_declination);
         _mag_earth.y = sinf(_last_declination);
@@ -740,7 +740,7 @@ AP_AHRS_DCM::drift_correction(float deltat)
     // flat, but still allow for yaw correction using the
     // accelerometers at high roll angles as long as we have a GPS
     if (AP_AHRS_DCM::use_compass()) {
-        if (have_gps() && AP_Math::is_equal(gps_gain,1.0f)) {
+        if (have_gps() && is_equal(gps_gain,1.0f)) {
             error[besti].z *= sinf(fabsf(roll));
         } else {
             error[besti].z = 0;