Revert "core: set RLIMIT_CORE to unlimited by default"

Revert "core: set RLIMIT_CORE to unlimited by default"

Partially revert commit 15a900327ab as this completely breaks core dumps
without systemd-coredump. It's also contradicting core(8), and it's not
systemd's place to redefine the kernel definitions of core files.

Commit bdfd7b2c now honours the process' RLIMIT_CORE for systemd-coredump. This
isn't what RLIMIT_CORE is supposed to do (it limits the size of the core
*file*, but the kernel deliberately ignores it for piping), so set a static
2^63 core size limit for systemd-coredump to go back to the previous behaviour
(otherwise the change above would break systemd-coredump).

Bug-Debian: https://bugs.debian.org/815020

Gbp-Pq: Topic debian
Gbp-Pq: Name Revert-core-set-RLIMIT_CORE-to-unlimited-by-default.patch