refactor: remove redundant migrations

[alan-agius4]

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This is a bulk delete of old migrations that cannot be executed when running ng update. This is because multiple version updates is not allowed for @angular/ packages. Ie: projects cannot update from v13 to version v15. Thus, the version 15 binary can only execute the update schematic to update from version 14 to version 15, which makes the older migrations unused redundant to be included in the NPM binary.