Proto/gas: fix timelock benchmarks Fixes #1598

Context

Applying suggestions proposed in !3160 (comment 633851800), which also fixes a discrepancy in the way workload is calculated between the benchmarks and the protocol.

Also remove unnecessary comments, and annotate gas values in michelson_v1_gas.ml that need to be benched.

Manually testing the MR

Launch the benchmarks

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, the Development Version section of CHANGES.md for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR