Remove support for _init and _fini in statically linked executables

These are legacy predecessors of .init_array/.fini_array. They were
already not supported by the dynamic linker.

src/header/stdlib/mod.rs

@@ -355,8 +355,6 @@ pub unsafe extern "C" fn exit(status: c_int) -> ! {
     unsafe extern "C" {
         static __fini_array_start: extern "C" fn();
         static __fini_array_end: extern "C" fn();
-
-        fn _fini();
     }
 
     for i in (0..unsafe { ATEXIT_FUNCS.unsafe_ref().len() }).rev() {
@@ -373,11 +371,6 @@ pub unsafe extern "C" fn exit(status: c_int) -> ! {
         (unsafe { *f })();
     }
 
-    #[cfg(not(target_arch = "riscv64"))] // risc-v uses arrays exclusively
-    {
-        unsafe { _fini() };
-    }
-
     unsafe { ld_so::fini() };
 
     unsafe { crate::pthread::terminate_from_main_thread() };