Simplify, drop ifdef: let if: become ifdef

Post audit, concensus is to drop if: and always do post-eval of all
ifdef: statements.  Also, rename ifdef: to if: for completeness.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/conf.c

@@ -1070,7 +1070,7 @@ int conf_reload(void)
 	/* Mark any reverse deps as chenaged. */
 	service_update_rdeps();
 
-	/* Prune according to ifdef:[!]ident */
+	/* Prune according to if:[!]ident or if:<[!]cond> */
 	service_mark_unavail();
 
 	/* Set up top-level cgroups */