Fix CI build error from dtslint

[ryanio]

Description

This PR fixes intermittent CI build failures due to dtslint erroring out on installing TypeScript 3.9.

As a workaround we install the latest typescript into each package and use the --localTs option. It's not ideal since we only test the types against one version, but it was the existing behavior prior to #3464 where I attempted to expand it. This PR also removes the now unnecessary // Minimum TypeScript Version comments I put in to satisfy testing against prior versions in that PR.

This PR also removes the devDep definitelytyped-header-parser sincedtslint automatically includes it as a child dep and outdated pinned versions may cause future dtslint issues.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have selected the correct base branch.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I ran npm run dtslint with success and extended the tests and types if necessary.
• I ran npm run test:unit with success.
• I have executed npm run test:cov and my test cases do cover all lines and branches of the added code.
• I ran npm run build-all and tested the resulting file/'s from dist folder in a browser.
• I have updated the CHANGELOG.md file in the root folder.
• I have tested my code on the live network.

[cgewecke]

Sweet. LGTM.