Remove MMAPv1 code

SERVER-35524 Remove queryable MMAPv1 storage engine

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• Closed

SERVER-20299 Delete KEEP_MUTATIONS stage

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• Closed

DOCS-11900 Docs for SERVER-35112: Remove MMAPv1 code

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SERVER-43075 MongoDB 4.2 cannot use storage.journal.commitIntervalMs param in yaml config file.

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SERVER-19576 Ability to select which storage engines to build (Wiredtiger or MMAPv1)

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