ftrace: Remove unused list 'ftrace_direct_funcs'

Commit 8788ca16 ("ftrace: Remove the legacy _ftrace_direct API")
stopped using 'ftrace_direct_funcs' (and the associated
struct ftrace_direct_func).  Remove them.

Build tested only (on x86-64 with FTRACE and DYNAMIC_FTRACE
enabled)

Link: https://lore.kernel.org/linux-trace-kernel/20240504132303.67538-1-linux@treblig.orgSigned-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

include/linux/ftrace.h

@@ -83,7 +83,6 @@ static inline void early_trace_init(void) { }
 
 struct module;
 struct ftrace_hash;
-struct ftrace_direct_func;
 
 #if defined(CONFIG_FUNCTION_TRACER) && defined(CONFIG_MODULES) && \
 	defined(CONFIG_DYNAMIC_FTRACE)

kernel/trace/ftrace.c

@@ -5318,14 +5318,6 @@ ftrace_set_addr(struct ftrace_ops *ops, unsigned long *ips, unsigned int cnt,
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 
-struct ftrace_direct_func {
-	struct list_head	next;
-	unsigned long		addr;
-	int			count;
-};
-
-static LIST_HEAD(ftrace_direct_funcs);
-
 static int register_ftrace_function_nolock(struct ftrace_ops *ops);
 
 /*