MINOR: 51d: Added dummy libraries for the 51Degrees module for testing.

MINOR: 51d: Added dummy libraries for the 51Degrees module for testing.

These are intended for use by HAProxy developers to ensure any changes
did not affect the 51Degrees implementation. The 51Degrees module can be
enabled and used by using the source in contrib/51d. This will run
without breaking, but will not return any meaningful information.

This is ideal for testing HAProxy core code, and other modules alongside
51Degrees, but should never be used as an actual module as it does
nothing.