[Serializer] Remove redundant normalizers document

[HypeMC]

The serializer/normalizers.rst document doesn't really contain any data that isn't already present in components/serializer.rst so I'd suggest removing it.

There was only one reference to it in serializer.rst but that document already contains a link to the Normalizers section in components/serializer.rst.

[javiereguiluz]

@HypeMC thanks a lot for this contribution. We love removing superfluous docs!

Please note that when we delete some page, we set up an HTTP redirection to the new contents to avoid 404 errors. I did that while merging (see e57adef)

[HypeMC]

Please note that when we delete some page, we set up an HTTP redirection to the new contents to avoid 404 errors. I did that while merging (see e57adef)

I wasn't aware of that, thanks for the info & help 😄