TASK: Remove shallow `ContentGraphProjection` decorator

[mhsdesign]

Upgrade instructions

Review instructions

The ContentGraphProjection didnt add anything but complexity. It was only used by the doctrine dbal impl but not from the postgres client because it turns out the concept is overhauled. Its just a dead decorator with no apparent use.

Checklist

• [ ] Code follows the PSR-2 coding style
• [ ] Tests have been created, run and adjusted as needed
• [ ] The PR is created against the lowest maintained branch
• [ ] Reviewer - PR Title is brief but complete and starts with FEATURE|TASK|BUGFIX
• [ ] Reviewer - The first section explains the change briefly for change-logs
• [ ] Reviewer - Breaking Changes are marked with !!! and have upgrade-instructions

[mhsdesign]

I guess this can be merged before stale again // cc @kitsunet ?