Move qcheck to the proper place

[edwintorok]

XAPI (wsproxy) already depended on qcheck, but only uses qcheck-core. We now have a package that uses 'qcheck' (not qcheck-core), which passes on the external CI, but fails on the internal CI.

@GabrielBuica this is needed to fix a build failure in the internal CI.

[psafont]

#=== ERROR while compiling safe-resources.master ==============================#
# context              2.1.6 | linux/x86_64 | ocaml-base-compiler.4.14.1 | git+file:///home/runner/work/xs-opam/xs-opam
# path                 ~/work/xs-opam/xs-opam/_opam/.opam-switch/build/safe-resources.master
# command              ~/.opam/opam-init/hooks/sandbox.sh build dune runtest -p safe-resources -j 4
# exit-code            1
# env-file             ~/.opam/log/safe-resources-11815-c8fcea.env
# output-file          ~/.opam/log/safe-resources-11815-c8fcea.out
### output ###
# File "ocaml/libs/sexpr/test/dune", line 4, characters 12-17:
# 4 |  (libraries sexpr astring rresult qcheck alcotest threads))
#                 ^^^^^
# Error: Library "sexpr" not found.

the new test added needs to define a package @GabrielBuica

[psafont]

The error can be fixed by merging xapi-project/xen-api#5684