stress-ng: update to 0.21.04

stress-ng: update to 0.21.04

Refresh PKG_HASH from the release tarball. Drop
001-allow-external-library-checks-to-be-disabled.patch: its check_lib /
check_lib_apparmor mechanism is upstream as of 0.21.04, so emptying a
LIB_* variable already skips that library check and the Makefile's
LIB_*= opt-out keeps working without the patch.

Pin the new LIB_NL and LIB_GENL probes off: 0.21.04 added netlink
stressors that would otherwise link libnl from staging_dir without a
corresponding DEPENDS, making the build non-deterministic.

Signed-off-by: Alexandru Ardelean <redacted>