Why is usetime always emitting for :clj

[lgrapenthin]

After this change, https://github.com/cgrand/macrovich/commit/f5a0e9d0c0e569361918231bf84b42eb1702689d , it appears that (usetime ...) always emits code in a .clj context, including ClojureScript macros. But then the emitted code is visible in macro phase.