Don't declare elf_sym_fns_lazy_psyms

Don't declare elf_sym_fns_lazy_psyms

An earlier patch neglected to delete a forward declaration of
elf_sym_fns_lazy_psyms.  This is no longer defined.  This patch
removes it.

gdb/ChangeLog
2021-03-27  Tom Tromey  <tom@tromey.com>

	* elfread.c (elf_sym_fns_lazy_psyms): Don't declare.