Remove unneeded Sphinx templates and static files (#9712)

These files are several files left over from old versions of the
documentation, and several from before `qiskit-sphinx-theme` was
entirely separate from the Terra docs-build process.  Having them remain
in the repository causes local (or CI) builds of the documentation to
pull from these templates instead of those provided by the theme
package, which causes us to get different behaviour to what will
actually be deployed during the metapackage docs build.

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
(cherry picked from commit 40f73a3)