tests: fix usage of require_ulimit_

tests: fix usage of require_ulimit_

* init.cfg (require_ulimit_v_): Renamed from require_ulimit_
as this only checks for ulimit -v support.  Other uses of
ulimit -t and ulimit -n in tests shouldn't cause false failures
if not supported.
* cfg.mk (sc_prohibit_test_ulimit_without_require_): A new syntax check
to ensure that require_ulimit_v_() is used iff required.
* tests/misc/head-c.sh: Add missing call to require_ulimit_v_.
* tests/rm/many-dir-entries-vs-OOM.sh: Likewise.
* tests/split/r-chunk.sh: Remove non mandatory require_ulimit_ call.
* tests/misc/sort-merge-fdlimit.sh: Likewise.
* tests/cp/link-heap.sh: Adjust to renamed require_ulimit_v_.
* tests/dd/no-allocate.sh: Likewise.
* tests/misc/csplit-heap.sh: Likewise.
* tests/misc/cut-huge-to-eol-range.sh: Likewise.
* tests/misc/printf-surprise.sh: Likewise.