[AGENTRUN-143] Remove dependencies disabling dead code elimination

[pgimalac]

Description

Remove the following dependencies from the Agent:

• github.com/cheggaaa/pb/v3
• github.com/xeipuuv/gojsonschema
• github.com/csaf-poc/csaf_distribution/v3

Motivation

Those three dependencies indirectly use reflect.Type.MethodByName (either through templates or directly), which disables dead code elimination in the agent.
I believe none of them is actually needed for the Agent so just removing the associated code is the simplest way to get rid of them.

Additional notes

Some of the dependencies are not removed from the go.mod because they are used in other files, but the changes in this PR are enough to remove them from the agent itself.

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).