Find and remove any unused internal/private classes.

Here is list of candidates, that needs to be reviewed carefully:

AsyncQueue
PositionalOperatorProjectionDefinition
ReflectionHelper
ExpressionToFindProjectionTranslator (from MongoDB.Driver.Linq.Linq3Implementation.Translators.ExpressionToFindProjectionTranslators namespace)
ExpressionReplacer
NoopBinaryDocumentFieldCryptor
WriteWireProtocolBase
IWireProtocol (non-generic one)
DelayedEvaluationWriteConcernSerializer
BulkUnmixedWriteOperationEmulatorBase
ReadAheadEnumerable
EnvironmentVariableProvider