Wunused-variable: Fixed all unused variables in src

This commit addresses all warnings emitted from -Wunused-variable
in the C++ src.

Signed-off-by: Noel Eck <noel.eck@intel.com>

src/grovescam/grovescam.cxx

@@ -98,7 +98,6 @@ bool GROVESCAM::dataAvailable(unsigned int millis)
       timeout.tv_usec = (millis % 1000) * 1000;
     }
 
-  int nfds;  
   fd_set readfds;
 
   FD_ZERO(&readfds);