fix(schema): Remove unsupported entities

[azlam-abdulsalam]

Description

Remove not supported entities from sfdx-project.json schema, such as

• postInstallScript
• uninstallScript
• unpackagedMetadata

These will be reintroduced at a later stage, when sfpowerscripts support it.

Workarounds:

• For postInstallScript utilize postDeploymentScript
• uninstallScript not currently supported
• unpackagedMetadata not currently supported

Checklist

All items have to be completed before a PR is merged

• Adhere to Contribution Guidelines
• Updates to Decision Records considered?
• Updates to documentation at DX@Scale Guide considered?
• Tested changes?
• Unit Tests new and existing passing locally?

[codecov-commenter]

Codecov Report

Merging #921 (e6d53a8) into develop (ccd0e79) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #921   +/-   ##
========================================
  Coverage    80.16%   80.16%           
========================================
  Files           36       36           
  Lines         1104     1104           
  Branches       238      238           
========================================
  Hits           885      885           
  Misses         209      209           
  Partials        10       10           

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[yippie]

Can we please immediately undo this. This change is effectively BLOCKING native salesforce package features for no reason. I believe sfpowerscripts simply calls force:package:version:create in the backend which means these tags WERE supported fully and removing them is literally blocking a native salesforce feature for no reason.