kprobes: Use IS_ENABLED() instead of kprobes_built_in()

Use IS_ENABLED(CONFIG_KPROBES) instead of kprobes_built_in().
This inline function is introduced only for avoiding #ifdef.
But since now we have IS_ENABLED(), it is no longer needed.

Link: https://lkml.kernel.org/r/163163038581.489837.2805250706507372658.stgit@devnote2



Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>