Remove all outdated entries from backports_required_for_multiversion_tests.yml

https://github.com/mongodb/mongo/blob/master/etc/backports_required_for_multiversion_tests.yml

From steven.vannelli@mongodb.com 

Steven Vannelli  2:13 PM
Alrighty, I got some more context from Vishnu. I understand this a little better now. Here's the summary: * When engineers commit something into master that will cause a multi version test to fail, they will make an entry into that file to exclude that test as part of the same commit.

• That test will not run until that ticket is backported to the older version the multi version test runs against (let’s say 6.0). As part of that backport commit, the engineer will add the same entry as the one on master on the 6.0 version of that file.
• If that entry exists in both versions of the file, it will start running. So as soon as that backport is merged in, the tests will run again. So we’ll need to do a diff between the two versions of the file.
• These are the ones we want to remove, since having an entry in both versions of the file does the same thing as not having them in either.

Hope that clarifies things! But let me know if anything is still in question.