ctdb-tests: Drop unreachable code

ctdb-tests: Drop unreachable code

This generates ShellCheck warnings:

In ./tests/UNIT/eventscripts/scripts/60.nfs.sh line 412:
			if [ -n "$service_check_cmd" ]; then
                                 ^----------------^ SC2031 (info): service_check_cmd was modified in a subshell. That change might be lost.

In ./tests/UNIT/eventscripts/scripts/60.nfs.sh line 413:
				if eval "$service_check_cmd"; then
                                         ^----------------^ SC2031 (info): service_check_cmd was modified in a subshell. That change might be lost.

service_check_cmd will never be set here because it is only set in a
sub-shell in rpc_set_service_failure_response().

This reverts some of commit 713ec217507d2f0d5f516efc45c8cd8773fccc14.

If testcases requiring use of service_check_cmd are later added then
this will need to be redone properly.  This would probably start by
renaming this function nfs_iterate_rpc_test().

Signed-off-by: Martin Schwenke <mschwenke@ddn.com>
Reviewed-by: Andreas Schneider <asn@samba.org>