tools: enable no-else-return ESLint rule
If an if block contains a return statement, the else block becomes unnecessary. Its contents can be placed outside of the block.
Refs: http://eslint.org/docs/rules/no-else-return
Inspired by https://github.com/nodejs/node/pull/11148
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
tools test lib benchmark