Cannot read property 'useCertificateStore' of undefined

[StephenWeatherford]

Seeing this in telemetry from multiple users. Only way I know to repro is

"docker.importCertificates": null

which shows an error but still gets passed through to our code. Maybe there's some other way as well.

[StephenWeatherford]

Still getting this in the 0.5.2 telemetry

[bwateratmsft]

This property is no longer used so this should be fixed.