We already set these variables and call `_init` in the dynamic linker.
As we don't care about static binaries, remove these assignments and the
call to `_init` from `_entry`.
The function referenced by DT_INIT is also not necessarily called
`_init`, so directly calling `_init` is not really correct.
`s_global_initializers_ran` and `__stack_chk_guard` are unused, so
remove them.