cleanup: remove dead forward declarations

src/errinj.h

@@ -60,9 +60,6 @@ bool errinj_get(int id);
 void errinj_set(int id, bool state);
 int errinj_set_byname(char *name, bool state);
 
-struct tbuf;
-void errinj_info(struct tbuf *out);
-
 typedef int (*errinj_cb)(struct errinj *e, void *cb_ctx);
 int errinj_foreach(errinj_cb cb, void *cb_ctx);
 

src/main.h

@@ -37,8 +37,6 @@
 extern "C" {
 #endif /* defined(__cplusplus) */
 
-struct tbuf;
-
 const char *tarantool_version(void);
 /**
  * Get version (defined in PACKAGE_VERSION), packed into uint32_t