Trivial: Remove execute bit from plain text files in git

[ctubbsii]

Trivially change file mode from 755 to 644 for files in git that
shouldn't be marked as executable. These were probably marked as
executable due to some contributors developing on Windows using a
filesystem that doesn't support POSIX file modes, or aggressively marks
everything as executable.

• Did you create an Apache Jira ticket? (not required for trivial changes)
• If a ticket exists: Does your pull request title follow the pattern "THRIFT-NNNN: describe my issue"?
• Did you squash your changes to a single commit? (not required, but preferred)
• Did you do your best to avoid breaking changes? If one was needed, did you label the Jira ticket with "Breaking-Change"?
• If your change does not involve any code, include [skip ci] anywhere in the commit message to free up build resources.

[ctubbsii]

I'm not sure what to make of that single Travis CI failure. It doesn't seem likely that it's related to this, but I don't understand why it failed.