ctf: Remove unused function prototype for getpname()

This function prototype should have been removed along with the
implementation.

Fixes:		3dd5524264 ctfdump: Use getprogname()
MFC after:	1 day

cddl/contrib/opensolaris/tools/ctf/common/utils.h

@@ -42,8 +42,6 @@ extern "C" {
 extern void vdie(const char  *, va_list);
 extern void die(const char *, ...);
 
-extern const char *getpname(void);
-
 #ifdef	__cplusplus
 }
 #endif