Revert Docsy card- and tabpane-shortcode style workarounds

#1027 introduced the following style workaround https://github.com/google/docsy/compare/v0.4.0...grpc:grpc.io-docsy:grpc.io-upto-doccsy-0.4.0#diff-1f4d7b8618cd04fd8c5bf1b1dc08c5ae99ade3e2418c79d1e8f2acaa07a90923:

>

Undo this override once the original issue (https://github.com/google/docsy/issues/1154) is fixed and merged into `grpc.io-docsy`.

Start by reviewing issue #1027 and the linked Docsy comparison to identify the card- and tabpane-shortcode style overrides. Check the status of Docsy issue #1154 and its merge into grpc.io-docsy; done means those workarounds are removed once the upstream fix is available.

Written by the indexing model from the issue text.