Require libgpg-error 1.24 and libassuan 2.4.2

* src/util.h (GPG_ERR_FALSE): Remove due to newer libgpg-error.

We require these over one year old versions to better allign with
GnuPG's demand. Note that the required libassuan is acgtually 2 years
old.

• Signed-off-by: Werner Koch <wk@gnupg.org>