`gz-sim9.pc` has a superfluous `Require: gz-cmake4`

[tho-]

Hi,

AFAICT, gz-cmake4 is not required to build against gz-sim9. This seems to be a build dependency only.
However, gz-sim9.pc mentions it in its Require: field.

This makes any application that has gz-sim9 as a dependency and looks for it with pkg-config require the installation of gz-cmake4. While not dramatic, this is not required. Unless I missed something, I think that extra Require could be dropped.

Note that this applies to all gz-*.pc files for all the dependencies of gz-sim9.pc, but I don't think opening an issue for each one is relevant :)