Make the generate.sh script delete the C structures folder before regenerating it.

generate.sh

 export PYTHON_PATH=${PWD}
 
+rm -R mavlink_skyward_lib/mavlink_lib
+mkdir mavlink_skyward_lib/mavlink_lib
 python -m pymavlink.tools.mavgen --lang C --wire-protocol 1.0 -o mavlink_skyward_lib/mavlink_lib mavlink_skyward_lib/message_definitions/skyward.xml