Removed Policy Groups 22, 19, 18, and 12 andPolicy 15.2 from Gmail Baseline per Issue 137

[jkaufman-mitre]

Based on the comments in issue #137, the following policies have been removed from the baseline:

• Policy Group 22
• Policy Group 19
• Policy Group 18
• GMAIL.15.2v0.1
• Policy Group 12

The remaining affected policies have been renumbered.

Fixes #137

[jkaufman-mitre]

Fixed the drift rules file. This PR Fixes #137

[tmcomeau]

Double check the table in the introduction for traceability.

[jkaufman-mitre]

Fixed Table of Contents at beginning.

[LaurenBassett]

It doesn't look like the tests have been updated.

[adhilto]

Marking as blocked until #132 is complete. When that is done I can make the needed code changes here.

[adhilto]

@LaurenBassett, I've made the needed Rego changes in this branch. Could you review my code changes? Note that because of how I merged the latest from main into here, it's showing a ton of changes. To see just my changes, under the "Files changed" tab, you can select "Changes from all commits" and change it to just my commit, "Remove deleted controls from the rego" (cb6db95).

EDIT: actually David helped me clean up the PR, it should now only be showing the relevant changes.