RFR: JDK-8238503 Remove unused field and accessor for docLocale from ToolOptions

[Jonathan Gibbons]

Please review a cleanup to remove some dead code and improve comments
for the tool options that are implemented in Start.preprocess.

No intentional change in functionality.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8238503
Webrev: http://cr.openjdk.java.net/~jjg/8238503/webrev/index.html