tests: remove useless sleep from tests on remake rules

tests: remove useless sleep from tests on remake rules

The sleeps were there to make generated autotools files strictly
newer than their sources; however, this is not necessary, since
POSIX mandates that make considers files with the same timestamp
of their dependencies to be up-to-date.

* tests/remake9a.test: Remove useless $sleep.
* tests/remake9b.test: Likewise.
* tests/remake9c.test: Likewise.
* tests/remake9d.test: Likewise.
* tests/remake10a.test: Likewise.
* tests/remake10b.test: Likewise.
* tests/remake10c.test: Likewise.