Remove unused #include <math.h>

Found with iwyu.

rigs/dummy/rot_pstrotator.c

@@ -20,7 +20,6 @@
 
 #include <stdlib.h>
 #include <string.h>  /* String function definitions */
-#include <math.h>
 #include <sys/time.h>
 #include <errno.h>
 

rigs/flexradio/smartsdr.c

@@ -22,7 +22,6 @@
 
 #include <stdint.h>
 #include <stdlib.h>
-#include <math.h>
 
 #include "hamlib/rig.h"
 #include "parallel.h"
@@ -670,4 +669,4 @@ int smartsdr_stop_morse(RIG *rig, vfo_t vfo)
 
     RETURNFUNC(retval);
 
-}
+}

rotators/flir/flir.c

@@ -23,7 +23,6 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>  /* String function definitions */
-#include <math.h>
 #include <sys/time.h>
 
 #include "hamlib/rotator.h"