Remove `type` from infrastructure blocks

[desertaxle]

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Prefect Version

2.x

Describe the proposed behavior

The type field on infrastructure blocks is removed and the block type slug is used in it's place.

Describe the current behavior

The type field on infrastructure blocks is unnecessary with the addition of block type slugs. The type currently matches the block type slug (e.g. docker-container for the DockerContainer block) and the block type slug can be used instead to remove an unnecessary field from the block document creation form for those block types.

Example Use

No response

Additional context

No response

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