Cleanup: move function to file where it is used

`drawLine` is only used for constraint, so it should be in
`transform_constraints.c`

source/blender/editors/transform/transform.h

@@ -809,8 +809,6 @@ void postTrans(struct bContext *C, TransInfo *t);
 void resetTransModal(TransInfo *t);
 void resetTransRestrictions(TransInfo *t);
 
-void drawLine(TransInfo *t, const float center[3], const float dir[3], char axis, short options);
-
 /* DRAWLINE options flags */
 #define DRAWLIGHT 1