Remove pricing from Proton Mail card

[matchboxbananasynergy]

This PR removes the mention of a specific price for Proton Mail, as we've recently opted to remove specific pricing from the website to make things easier to maintain.

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[github-actions]

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[blacklight447]

Where is the discussion about this removal?

[matchboxbananasynergy]

@blacklight447

Initial discussion turned issue:
#1737

PR where some comments where made and after discussion it was decided that it makes sense to just link to the websites and let people find the pricing from the source:
https://github.com/privacyguides/privacyguides.org/pull/1806

PR that removed pricing from existing cards:
#1811

Listing the pricing ourselves is hard to maintain, as a long of services change their prices, or have sales etc. Furthermore, we used to list some prices in EUR and some prices in USD which was inconsistent. Also, some services support multiple different currencies, so by only listing one, we might be giving people the wrong idea about that.

This PR just addresses an instance where we mention pricing that was overlooked in the PR that removed it from most places.

[privacyguides-bot]

This pull request has been mentioned on Privacy Guides. There might be relevant details there:

https://discuss.privacyguides.org/t/v2-27/1084/1