This commit cleans up Javadoc that does not add information.
It resolves ecj warnings:
 `Javadoc: Description expected after ...`
It helps to prevent future empty javadoc by disabling
missingJavaDoc warnings. This resolves
 `Javadoc: Missing ...`

The modification is a result of regular expression search&replace:

in files `*.java` (exclude org.eclipse.jdt.core.tests.model/workspace)
 `^[\s]*\*[\s]*(@return|@param[\s]*[^\s]+|@throws[\s]*[^\s]+)\R([\s]*\*[\s]*@|[\s]*\*/\R)`
 ->`$2`
 `^([\s]*\*[\s]*\R)([\s]*\*/\R)`
 ->`$2`
 `^[\S\t]*/\*\*\R[\s]*\*/\R`
 ->``

in files `org.eclipse.jdt.core.prefs`
 `org\.eclipse\.jdt\.core\.compiler\.problem\.missingJavadoc(Comments|Tags)\=[^\s]*`
 ->`org\.eclipse\.jdt\.core\.compiler\.problem\.missingJavadoc$1\=ignore`