Replace instances of `.. page::` with:
```rst
.. raw:: pdf
PageBreak
```
This reduces my usage on the `preprocess` functionality I'd like to
remove.
This was done by executing this command:
```
find src -type f -name '*.rst' \
-exec sed -Ei 's/.. page::$/.. raw:: pdf\n\n PageBreak/g' {} \;
```
The canonical versions of my style files are stored within `src/styles`,
and these are the ones that should be used as they have the latest
changes and have been converted to the YAML format.
This commit removes any styles within the individual talk directories.
