Proto: fix ignored values (part 3/3)

Context

It is always dangerous to ignore values. They may be:

• partial applications that we wanted to be fully applied,
• monadic values that should have been bound,
• states that should be handled linearly (e.g. the context).

This MR removes the pattern >[^ ]* fun _[^ ]* -> from lib_protocol. !6577 (merged) and !6579 (merged) take care of (monadic) let.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR