Remove Windows 1803 support

Overview

Currently, we have 1803 Windows support and we run tests on that version as well which are flaky and time consuming.

According to https://support.microsoft.com/en-us/lifecycle/search?alpha=1803 https://support.microsoft.com/en-us/lifecycle/search?alpha=1803 is not longer supported since 18 months has passed becuase it's part of the Semi-Annual Channel. The only supported version is Windows 10, version 1803 (Enterprise, Education, IoT Enterprise) now if we support that version or not I'm not sure we have discussed this in !1533 (merged)

Now if we remove support for 1803 we might break support for Windows 10, version 1803 (Enterprise, Education, IoT Enterprise) (needs to be validated)

Proposal

• Remove 1803 tests
• Remove 1803 from supported version
• Remove 1803 helper images builds