vsh: Make vshInitDebug static

There's no reason why debug initialization could not be made completely
hidden, just like readline initialization is. The point of the global
initializer vshInit is to make initialization of smaller features transparent
to the user/caller.

tools/vsh.c

@@ -2680,7 +2680,7 @@ vshReadline(vshControl *ctl, const char *prompt)
 /*
  * Initialize debug settings.
  */
-void
+static void
 vshInitDebug(vshControl *ctl)
 {
     const char *debugEnv;

tools/vsh.h

@@ -305,7 +305,6 @@ void vshPrintExtra(vshControl *ctl, const char *format, ...)
 bool vshInit(vshControl *ctl, const vshCmdGrp *groups, const vshCmdDef *set);
 bool vshInitReload(vshControl *ctl);
 void vshDeinit(vshControl *ctl);
-void vshInitDebug(vshControl *ctl);
 void vshDebug(vshControl *ctl, int level, const char *format, ...)
     ATTRIBUTE_FMT_PRINTF(3, 4);