Merge pull request #70036 from bluikko/wip-doc-remove-rtd-sphinx-search

doc: remove unsupported readthedocs-sphinx-search

Reviewed-by: Anthony D'Atri <anthony.datri@gmail.com>
Reviewed-by: Dan Mick <dan.mick@redhat.com>
Reviewed-by: Kefu Chai <k.chai@proxmox.com>