[Smell] JavaModelManager.shutdown() join on Job family that seems unused

[mickaelistria]

While working on #1190 and investigating the behavior of JavaModelManager, I noticed that its shutdown method calls JobManager.join(JavaCore.PLUGIN_ID,...) to "wait for the initialization job to finish". However, it looks like nowhere in JDT Core a job is created with a belongsTo that makes it part of the JavaCore.PLUGIN_ID. So it looks like this join is a no-op and could be removed; or that an important job misses instructions to be part of this JavaCore.PLUGIN_ID family.

[jukzi]

Looks more like the JavaCore.PLUGIN_ID is not used as family where it should

					public boolean belongsTo(String jobFamily) {
						return true;
					}

As used in JavaModelManager and SearchableEnvironment and PatternSearchJob matchs the JobFamily JavaCore.PLUGIN_ID - and every other family.