mac ci: Drop pkg-config install step

[kazarmy]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository
• I made sure to follow the project's coding style
• I've documented or updated the documentation of every function and struct this PR changes. If not so I've explained why.
• I've added tests that prove my fix is effective or that my feature works (if possible)
• I've updated the rizin book with the relevant information (if needed)

Detailed description

On mac builds, this pr drops the pkg-config install step because it's not necessary:

(https://github.com/rizinorg/rizin/actions/runs/11477136912/job/31938591776#step:4:1)

Test plan

The drop is appropriate. All builds are green.

Closing issues

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