*: introduce and use bb_unsetenv_and_free

function                                             old     new   delta
bb_unsetenv_and_free                                   -      17     +17
tcpudpsvd_main                                      1819    1810      -9
safe_setenv                                           58      47     -11
udhcp_run_script                                     630     616     -14
make_device                                         1683    1663     -20
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/4 up/down: 17/-54)            Total: -37 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/miscutils/crond.c b/miscutils/crond.c
index f511592..4a3103c 100644
--- a/miscutils/crond.c
+++ b/miscutils/crond.c
@@ -264,8 +264,7 @@
 	char *var_val = *pvar_val;
 
 	if (var_val) {
-		bb_unsetenv(var_val);
-		free(var_val);
+		bb_unsetenv_and_free(var_val);
 	}
 	*pvar_val = xasprintf("%s=%s", var, val);
 	putenv(*pvar_val);