The new test/e2e/framework/testfiles package makes it possible to
write tests that do not depend on a specific way of providing
additional test files at runtime. Such tests and the framework are
then more easily reused in other test suites.

In the test/e2e suite file access is enabled based on the existing
"repo-root" command line parameter and the built-in bindata. Tests
using the new API will first check for files under "repo-root" and
then fall back to the builtin data. This way, users of a test binary
can modify those files without having to rebuild the binary.

"repo-root" is still needed because at least some tests check for
additional files (secret.yaml, via ingress_utils.go) that are not part
of the upstream source code and thus may or may not be built into a
test binary.

Tests using bindata or repo-root directly get modified to use the new
API, or removed when they are obsolete: test/e2e/examples.go depended
on files that were removed in
https://github.com/kubernetes/kubernetes/pull/61246 and thus can no
longer be run in Kubernetes. Moving the tests to kubernetes/examples
is tracked in https://github.com/kubernetes/examples/issues/214.

The file removal did not break the automated E2E testing probably
because the tests are under the Feature:Example tag and thus not
enabled during normal CI runs.

Removing also the obsolete tests makes it simpler to rework the
"repo-root" setting because less code uses it.

Related-to: #66649 and #23987