website/**/es: Remove es translation for website

It looks like that there is very little interest from the Spanish
developers about FreeBSD as there has not been any single commit on this
apart from the obvious ones:
https://cgit.freebsd.org/doc/log/website/content/es

Additionally our index page also do not point to the Spanish
translations although they do about de, fr, ja, zh-cn and zh-tw.

So I think it's better to kill it rather than serving old outdated
information. If there are more interests from the community we will
reconsider adding or resurrecting this.

Just to clarify this do not delete the es documentation and also have no
such intention to delete. The documentation will remain as is.

Approved by: carlavilla fernape
Differential Revision: https://reviews.freebsd.org/D41860