Improve translatable strings in WP.org Profiles Activity Handler

[SergeyBiryukov]

Let's fix a few translatable string issues in wporg-profiles-activity-handler.php:

• Strings with placeholders should have translator comments.
• Multiple placeholders should be numbered.
• Extra HTML code that does not need to be translated should be removed.
• Strings should be complete sentences, not a concatenation of separate phrases.

[coffee2code]

Thanks, @SergeyBiryukov!

However, after considering the strings, I ended up removing the ability for the strings to be translated in [3911].

All such strings were the activity action values (the strings that actually appear in the activity stream), which due to the design of BP's activity module, get stored in the database and not made dynamically, so translation is not appropriate.