Hi guix,

In the context of <https://issues.guix.gnu.org/49123>,
I'm improving the package definitions of some dependencies
of 'mirage'.

The git repo of libolm bundles a compiled (!) version of gradle.
libolm doesn't have a Java input, so it cannot be used accidentally
in Guix, but remove it anyways to be really sure.

This causes only two rebuilds, which succeeded on x86_64-linux.

Greetings,
Maxime.