Test implicit index & remove extraneous example file

[sc1f]

This PR adds tests in the core engine to assert that behavior around implicit __INDEX__ columns work as expected, in that updates with the __INDEX__ column should behave like partial updates on the row ID specified in __INDEX__.

• tests generation of implicit index column in to_format
• tests reading of implicit index for 0, 1, and 2-sided views
• removes extraneous schema.html in examples folder

[texodus]

Looks good, thanks for the PR!