Replace some eshell functions that duplicate standard functions.

Replace some eshell functions that duplicate standard functions.

* lisp/eshell/esh-util.el (eshell-time-less-p, eshell-time-to-seconds): Remove.
(eshell-read-passwd, eshell-read-hosts): Use time-less-p.
* lisp/eshell/esh-test.el (eshell-test, eshell-show-usage-metrics):
* lisp/eshell/em-unix.el (eshell-show-elapsed-time, eshell/time):
* lisp/eshell/em-pred.el (eshell-pred-file-time): Use float-time.
* lisp/eshell/em-ls.el (eshell-ls-sort-entries): Use time-less-p.