HmacSecret app_data not actually used

[rlpowell]

zero-to-production/src/startup.rs

Line 110 in 236cef0

.app_data(Data::new(HmacSecret(hmac_secret.clone())))

^^ AFAICT, by about 3/4 through Chapter 10, HmacSecret is not used in any way and that app_data line is irrelevant.

[LukeMathWalker]

Good catch!