Revert "Fix missing include".

Don't include <string> twice. Another include was introduced in 938e4ab0.

This reverts commit f1fd8f8f6a50e4be7797a5829062cb7649c6365a.
Merge pull request #26 from mrothe/patch-1

Revert "Fix missing include".
monitor_t: Avoid compiler warnings resulting from unused method parameters.
Merge pull request #27 from jonnydee/master

monitor_t: Avoid compiler warnings resulting from unused method parameters.