[java] Fix broken LICENSE link in java/README.md - #2553

The License section of java/README.md links to sdk/LICENSE, which resolves to java/sdk/LICENSE — a path that does not exist. The link 404s on GitHub.

No java-local LICENSE has ever been tracked in this repository, so the link has been dead since it was introduced; the java/src → java/sdk restructure in #2301 only changed which nonexistent path it pointed at (LICENSE → sdk/LICENSE). This retargets it to the repository-root ../LICENSE.

Verification

The only LICENSE files tracked in the repo:

$ git ls-files | grep LICENSE
LICENSE
rust/LICENSE

java/LICENSE was never tracked, so the pre-restructure link was dead too:

$ git log --oneline --all -- java/LICENSE
                      # (no output)
$ git ls-tree d9a6fabb^ java/ --name-only | grep LICENSE
                      # (no output — java/LICENSE absent before the move as well)

Before / after, resolved relative to java/README.md:

Scope

One line in one file. java/README.md is the only README that links to a LICENSE file — nodejs, go, and dotnet each render a bare MIT under ## License, and rust/python have no License section at all — so nothing else is affected.