Remove unused configure checks

* configure.ac (AC_CHECK_FUNCS): Remove _sys_siglist and sys_siglist.
(AC_CHECK_DECLS): Likewise.
diff --git a/configure.ac b/configure.ac
index fa4a4bd..be28ebe 100644
--- a/configure.ac
+++ b/configure.ac
@@ -206,8 +206,6 @@
 	stpcpy
 	strerror
 	strsignal
-	_sys_siglist
-	sys_siglist
 ]))
 AC_CHECK_HEADERS(m4_normalize([
 	asm/cachectl.h
@@ -260,7 +258,6 @@
 AC_CHECK_TYPES([struct flock64],,, [#include <fcntl.h>])
 
 AC_CHECK_DECLS([sys_errlist])
-AC_CHECK_DECLS([sys_siglist, _sys_siglist],,, [#include <signal.h>])
 AC_CHECK_DECLS(m4_normalize([
 	PTRACE_EVENT_CLONE,
 	PTRACE_EVENT_EXEC,