Fix build by removing linker flags

[james-ward]

Closes #294

[SteveMacenski]

Waiting on @Timple but LGTM.

[Timple]

Well, this check should not have false positives. But you are right, there is an issue upstream which causes this: ros2/rosidl_python#213

I would put these lines below the message generation, that also works. With a comment why this is at that location referencing the upstream issue.

But I'm also not against removing it as it's just an extra check preventing runtime linking issues.

[SteveMacenski]

That seems reasonable to me. @james-ward can you move it below the messages?

[Rayman]

@james-ward you can also move the linker flags after the messages are generated. Then we still get warnings from our own code, but not from the messages