Advance deprecation for `is.hms`/`as.hms`

[hadley]

Marked as deprecated_soft() in 0.5.0, need to be advanced to deprecate_warn().

[moodymudskipper]

The 'hms' package uses the 'lifecycle' package to handle the deprecation cycle.

From ? deprecate_soft :

• deprecate_soft() warns only if the deprecated function is called directly, i.e. a user is calling a function they wrote in the global environment or a developer is calling it in their package. It does not warn when called indirectly, i.e. the deprecation comes from code that you don't control.

• deprecate_warn() warns unconditionally.

• deprecate_stop() fails unconditionally.`

is.hms() and as.hms() contain calls to deprecated_soft() since some time, and it's time to use deprecated_warn() instead, this is a simple replacement (+ Update in the NEWS).