RFR: 8297041: Remove the last remnants of sjavac [v2]

[Magnus Ihse Bursie]

> The sjavac ("smart javac") was an ambitious project. It should parallelize java compilation, create a background daemon process that kept the JVM "hot" with the JITted javac code, define a public api so only noticeable changes in a class caused further dependency compilations, etc etc.
> 
> Some of this never came to fruition. Other were implemented differently, as the `depend` plugin. The only thing we're currently using (and have been for the last few years) is the "server" functionality, that is, the ability to keep a single JVM process alive, and reuse the JITted code.
> 
> This code does not belong in the jdk.compiler module. It is a buildtool, pure and simple. Let's move it to it's proper place.

Magnus Ihse Bursie has updated the pull request incrementally with two additional commits since the last revision:

 - Fix weird imports
 - Update comment

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/11185/files
  - new: https://git.openjdk.org/jdk/pull/11185/files/2124c86b..8ff38b78

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=11185&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=11185&range=00-01

  Stats: 77 lines in 15 files changed: 45 ins; 30 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/11185.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11185/head:pull/11185

PR: https://git.openjdk.org/jdk/pull/11185