Remove pygments from hugo config file

[SayakMukhopadhyay]

pygments configuration is no longer needed for Docsy (see google/docsy#2150). This should be true even for Docsy 0.5.1.

[sftim]

/kind cleanup
/remove-kind bug
/area web-development
/triage accepted
/priority backlog
/help

[k8s-ci-robot]

@sftim:
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/kind cleanup
/remove-kind bug
/area web-development
/triage accepted
/priority backlog
/help

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