Exempt MODULE.bazel from Library-Compliance requirement

Gerrit’s external Maven dependencies relevant for Library-Compliance are
now declared through the rules_jvm_external TOML input tools/deps.toml
and wired from tools/java_deps.MODULE.bazel.

tools/deps.toml already requires Library-Compliance approval. It is the
authoritative place for third-party library coordinates and versions
that are relevant for Google.

The root MODULE.bazel mostly declares Bazel modules and build rules,
such as rules_java, rules_nodejs, rules_jvm_external, and local module
wiring. These Bazel module dependencies are not the library dependencies
consumed by Google, and requiring Library-Compliance approval for every
MODULE.bazel change creates unnecessary review friction.

Keep Library-Compliance focused on the files that actually define
relevant external library metadata.

As part of this cleanup, also remove the obsolete maven_install.json
entry from the submit requirement. It was left over from the bzlmod
migration, and the file no longer exists.

Change-Id: I698df8ef0df5566af6d426db01f9bd15da89fda1