stop displaying time of build in online help

stop displaying time of build in online help

As part of the “reproducible builds” effort [1], we have noticed that
apt could not be built reproducibly.

One issue is that it uses the __DATE__ and __TIME__ macros of the C
preprocessor to display the time of build in the online help. We believe
this information not to be really useful to users as they can always
look at the package data and metadata to figure it out.

The attached patch simply removes this information. All
non-documentation packages can then be built reproducibly with our
current experimental framework.

[David: changed the string slightly to be untranslateable as well]

Closes: 774342