examples: remove old outdated examples (#1742)

Remove the build and submit examples, and the `examples` package.

Make it easier to update to multiple modules by removing top-level packages that do not contain useful code.

I'm going to be making a proposal to move some packages in the monorepo to support a successful versioning of our Go SDK alongside versioning of our services, tools, and experimental code, and this package either needs moving or removing. On inspection the package contains two small examples of using the old `build` package. We are currently recommending folks use `txnbuild` and so it seems not worthwhile to expend effort to keep.

I don't see any active docs that reference these examples either.