Declaration files should not emit accessor warnings

[weswigham]

In our docker suite, some declaration files are issuing errors along the lines of

dist-esm/ChangeFeedResponse.d.ts:25:9 - (TS1056) Accessors are only available when targeting ECMAScript 5 and higher.

this might be coming from an older version of TS, but if it's not, we need to remove this error, as it doesn't make sense to talk about accessor implementation limitations in declaration files.

[sandersn]

This is only an error in 3.5 and earlier in my experimentation. I'm working with @bterlson to decide how to support Azure SDK's outputs to 3.3-3.5; probably we'll end up with typesVersions for 3.5 and newer, plus an automatic rewrite.

Closing this bug since 3.6 and 3.7 do not emit this warning.