fix PrimaryIsNotServing logic

[deepthi]

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[deepthi]

I walked through this code with @GuptaManan100. The function is called PrimaryIsNotServing but it actually is trying to compute something else - whether we should start buffering queries in vtgate. I'm going to close this, Manan will create an issue that describes the problem this was trying to fix, and do a PR with the correct fix instead.