Use dummy bridge stub if fastrtpsgen not found

If the build config specifies RTPS topics to import/export and fastrtpsgen is not installed
on the build machine, then a dummy stub is used for the RTPS bridge.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

cmake/configs/nuttx_px4fmu-v4_default.cmake

@@ -207,8 +207,6 @@ set(config_module_list
 	examples/ekf_att_pos_estimator
 )
 
-set(GENERATE_RTPS_BRIDGE on)
-
 set(config_rtps_send_topics
    sensor_combined
    )

cmake/configs/posix_sitl_default.cmake

@@ -184,8 +184,6 @@ set(config_extra_builtin_cmds
 	sercon
 	)
 
-set(GENERATE_RTPS_BRIDGE on)
-
 set(config_rtps_send_topics
 	sensor_baro
 	)