refactor: Migrate the last 2 test_misc.sh cases to Bazel-native sh_test

[bor-p-s]

Description

#1921 migrated 5 of test/shell/test_misc.sh's 7 cases and left test_override_javabin and xmllint_test for a follow-up. This is that follow-up, and it deletes the file (and its test_rules_scala.sh line) for good.

test_override_javabin becomes a bespoke sh_test (test/override_javabin), following the same nested_bazel.sh pattern #1943 used for a bazel run-based case: it sets JAVABIN=/etc/basdf before a nested bazel run //test:ScalaBinary and asserts the run fails. None of the 4 expect_build_failure.bzl macros fit, since none of them wrap bazel run. JAVABIN is read by the bash launcher scala_binary/scala_test generate (phase_java_wrapper.bzl); on Windows Bazel uses a native .exe launcher instead that doesn't consult it, so the target is target_compatible_with-excluded there, matching the original's is_windows skip.

xmllint_test is dropped, not migrated. It validated that XML files under bazel-testlogs -- generated by every other test in the old shell suite's run -- were well-formed. That's not something one sh_test can check: it only sees its own run's output, not the whole suite's. The check itself was validating Bazel's own test-result XML output, which Bazel already treats as its own schema-versioned format to maintain; there's no known case of Bazel producing malformed test-result XML, so this looks like a leftover safety check rather than something specific to rules_scala.

Motivation

Release impact: tests only.