External dependencies break rosdep cli

[incebellipipo]

The qualisys_cpp_sdk dependency breaks rosdep

mocap4ros2_qualisys/qualisys_driver/package.xml

Line 19 in e76871d

<build_depend>qualisys_cpp_sdk</build_depend>

$ rosdep install --from-paths src -i
ERROR: the following packages/stacks could not have their rosdep keys resolved
to system dependencies:
qualisys_driver: Cannot locate rosdep definition for [qualisys_cpp_sdk]

It is correct that some non-ros dependencies can be handled using package.xml file, but this breaks automated installations. I suggest to remove this line. If that's ok, I will create a PR accordingly.

[incebellipipo]

This will be solved here: #6