avoid crash in imem.c plugin

p_sys is allocated using vlc_calloc but deleted by regular 'free' call.
This cause 'double free or corruption' crash.
do not delete p_sys here because it will be automatically deallocated by
'vlc_objres_clear' in modules.c
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>

modules/access/imem.c

@@ -257,7 +257,6 @@ static int OpenCommon(vlc_object_t *object, imem_sys_t **sys_ptr, const char *ps
 
     if (!sys->source.get || !sys->source.release) {
         msg_Err(object, "Invalid get/release function pointers");
-        free(sys);
         return VLC_EGENERIC;
     }