pacific: qa: drop the distro~HEAD directory from the fs suite.

It looks 01d85f9ba9264a89d8c031bc221928ef349aa602 accidentally
backed up the old `distro` directory into `distro~HEAD` instead
of just replacing it with new content. This makes possible to
have a teuthology job combining altogether e.g. `distro/{rhel_8}`
and `distro~HEAD/{ubuntu_latest} which leads to selection of
Ubuntu Bionic but without the necessary `exit_on_first_error: false`
override for Valgrind.

This commit fixes the problem by removing the extra `distro~HEAD`
directory. It applies solely to pacific as backport's source
(ec1b82fd24220a8cff442194ca98be9ed7ea1816) is free of the issue.

Fixes: https://tracker.ceph.com/issues/49962
Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

diff --git a/qa/suites/fs/verify/distro~HEAD b/qa/suites/fs/verify/distro~HEAD
deleted file mode 120000 (symlink)
index 78f2991..0000000
--- a/qa/suites/fs/verify/distro~HEAD
+++ /dev/null
@@ -1 +0,0 @@
-.qa/distros/supported-random-distro$/
\ No newline at end of file