kprobes: treewide: Replace arch_deref_entry_point() with dereference_symbol_descriptor()

~15 years ago kprobes grew the 'arch_deref_entry_point()' __weak function:

  3d7e3382: ("jprobes: make jprobes a little safer for users")

But this is just open-coded dereference_symbol_descriptor() in essence, and
its obscure nature was causing bugs.

Just use the real thing and remove arch_deref_entry_point().

Link: https://lkml.kernel.org/r/163163043630.489837.7924988885652708696.stgit@devnote2



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