Remove LoadGenesisDoc() in favor of GenesisDocFromFile()

[alessio]

Duplication of effort discovered while on #3130

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added a relevant changelog entry: sdkch add [section] [stanza] [message]
• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[alessio]

This should be listed as an improvement rather than a breaking change as it affects a gaia internal API. No SDK users should depend on gaia internal APIs

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@055d219). Click here to learn what that means.
The diff coverage is 0%.

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[alessio]

Superseded by #4063