Remove codec library classes

[alcaeus]

The CodecLibrary class was introduced as it was necessary when working with lazy BSON codecs. Since those have been removed from the 1.17 release, it does not make sense to introduce the library either, as there's no direct need for it. In fact, in most frameworks (e.g. Laravel, Symfony), each codec would rely on a service locator to receive codecs it needs for data types or embedded documents as a constructor dependency. Until we have a clear need for such functionality, it's best to not introduce code so we are not bound by any BC promises.

[GromNaN]

The architecture document needs to be updated.

mongo-php-library/src/Codec/architecture.md

Lines 33 to 39 in 30be2cd

	## Codec Libraries
	The `CodecLibrary` class is able to combine several `Decoder`, `Encoder`, and `Codec` instances into a single codec.
	When decoding or encoding a value, the library will use the first instance that supports the value. This allows for
	easier composition of codecs. A `Decoder`, `Encoder`, or `Codec` implementation may choose to implement the
	`KnowsCodecLibrary` interface. In this case, when the codec is added to a library, the library is injected into the
	instance using the `attachCodecLibrary` method. This allows the codec to use the library to decode or encode values.