Fix GH Actions Windows CI: switch from pkgconf to pkg-config

[amesgen]

Description

This fixes this CI error that has appeared recently.

MSYS2 recently updated (msys2/MINGW-packages#13257) its version of pkgconf, which is an alternative implementation of the "classic" pkg-config, with both providing the pkg-config binary. It seems that this does no longer work correctly (concretely, pkg-config --modversion pkg1 pkg2 pkg3 ... is supposed to output the version numbers for all arguments, but pkgconf returns at most two versions).

To fix this, I removed cmake (as it requires pkgconf), and we now install pkg-config manually, as putting it in the install block above causes it to be silently elided, as the mingw-w64-x86_64-toolchain group contains pkgconf.

Checklist

• Branch
  • Commit sequence broadly makes sense
  • Commits have useful messages
  • New tests are added if needed and existing tests are updated
  • If this branch changes Consensus and has any consequences for downstream repositories or end users, said changes must be documented in interface-CHANGELOG.md
  • If this branch changes Network and has any consequences for downstream repositories or end users, said changes must be documented in interface-CHANGELOG.md
  • If serialization changes, user-facing consequences (e.g. replay from genesis) are confirmed to be intentional.
• Pull Request
  • Self-reviewed the diff
  • Useful pull request description at least containing the following information:
    • What does this PR change?
    • Why these changes were needed?
    • How does this affect downstream repositories and/or end-users?
    • Which ticket does this PR close (if any)? If it does, is it linked?
  • Reviewer requested

[dnadales]

bors r+

[amesgen]

bors merge

[iohk-bors]

Already running a review

[iohk-bors]

Build succeeded:

• build (8.10.7, ubuntu-latest)
• build (8.10.7, windows-latest)
• ci/hydra:Cardano:ouroboros-network:required