remove redundant, too-early call to clearenv in api_start call.

Ok, took a look, what happened was the clearenv calls used to be
in lxc_start and lxccontainer and lxc_execute (do lxc_start() callers)
themselves.  I moved those into do_start(), but the calls in
lxccontainer.c were never removed.

They should simply be removed altogether.  Trivial patch follows.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>