Don't set java home per-configuration

[keynmol]

I've been seeing lots of issues with plugin/compile not working - even on a clean machine.
It'd work once, and then next invocation crashes:

[info] compiling 21 Java sources to /Users/antonsviridov/projects/sourcegraph/scip-java/semanticdb-javac/target/classes ...
[warn] Unexpected javac output: Unrecognized option: --add-exports
[warn] Error: Could not create the Java Virtual Machine.
[warn] Error: A fatal exception has occurred. Program will exit..
[warn] javac exited with exit code 1
[debug] Rolling back changes to class files.
[debug] Removing generated classes:
[debug] Restoring class files:
[debug] Removing the temporary directory used for backing up class files: /Users/antonsviridov/projects/sourcegraph/scip-java/semanticdb-javac/target/classes.bak
[error] (plugin / Compile / compileIncremental) javac returned non-zero exit code
[error] Total time: 0 s, completed 19 Apr 2023, 10:06:41

sbt:root> plugin/Compile/javaHome
[info] Some(/Users/antonsviridov/Library/Caches/Coursier/arc/https/cdn.azul.com/zulu/bin/zulu8.68.0.21-ca-jdk8.0.362-macosx_aarch64.tar.gz/zulu8.68.0.21-ca-jdk8.0.362-macosx_aarch64)

If one takes a look at the debug output, it's clear that for some reason javacOptions have changed between runs:

Randomly thrashing about I ended up removing the javaHome from per-configuration settings, to the global one.

Immediately I was successful in running plugin/compile multiple times without issue, along with rerunning tests without having to constantly clear the cache.

I cannot explain it, nor am I sure that this is the fix, but it's a pretty strong signal on my machine that this change fixes one of the issues I was having.

Test plan

CI shouldn't be affected by this change, manual testing confirms some improvements.