i18n: Spurious (and translatable) alt-text added to cards

[jpmckinney]

Describe the bug

Due to lines like:

https://github.com/executablebooks/sphinx-design/blob/42077cf08756019db3936fbd9a66d68f6ce6d23d/sphinx_design/cards.py#L117

My POT file contains, in this case:

msgid "card-img-top"
msgstr ""

Reproduce the bug

Run sphinx-build -b gettext docs _build (or whatever paths are appropriate) while using this package and using the img-background, img-top or img-bottom options.

List your environment

Not environment dependent.

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[chrisjsewell]

I believe this was closed in #114