busybox

ash: Remove unused EV_BACKCMD flag

    The original ash defered forking commands in backquotes so builtins
    could be run in the same context as the shell.  This behavior was
    controlled using the EV_BACKCMD to evaltree.

    Unfortunately, as Matthias Scheler noticed in 1999 (NetBSD PR/7814),
    the result was counterintuitive; for example, echo "`cd /`" would
    change the cwd.  So ash 0.3.5 left out that optimization.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>