CA-421991: Fix QEMU coredumps on XS9 (#6793)

On XS8, systemd's coredump handler ignores the process core rlimit so
QEMU coredumps work correctly.
On XS9, systemd's coredump handler respects the process core rlimit so
QEMU coredumps end up truncated to 64 MiB which prevents gdb from
loading them correctly.

Fix this by removing the setting of the core rlimit from the wrapper so
that it behaves like XS8. This is fine since the systemd coredump
handler ensures that the root fs will not run out of space.

Author: robhoes

ocaml/xenopsd/scripts/qemu-wrapper

@@ -65,16 +65,6 @@ def restrict_fsize():
     limit = 1024 * 1024
     setrlimit(RLIMIT_FSIZE, (limit, limit))
 
-def enable_core_dumps():
-
-    limit = 64 * 1024 * 1024
-    oldlimits = getrlimit(RLIMIT_CORE)
-    hardlimit = oldlimits[1]
-    if limit > hardlimit:
-        hardlimit = limit
-        setrlimit(RLIMIT_CORE, (limit, hardlimit))
-        return limit
-
 def xenstore_read(path):
     return xenstore.read("", path)
 
@@ -117,9 +107,6 @@ def prepare_exec():
             print("Warning: writing pid to '%s' cgroup.procs file: %s" \
                 % (cgroup_slice, e))
 
-    core_dump_limit = enable_core_dumps()
-    print("core dump limit: %d" % core_dump_limit)
-
     if not file_serial:
         restrict_fsize()