Remove explicitly set language mode
Remove explicitly set language mode

The default is now ECMASCRIPT_2017 (aka ECMAScript 8) and the language
versions will be advancing much more quickly in coming years.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=174788549

jart/rules_closure,jart/rules_closure,bazelbuild/rules_closure,bazelbuild/rules_closure,gramic/rules_closure,bazelbuild/rules_closure,gramic/rules_closure,gramic/rules_closure,jart/rules_closure,bazelbuild/rules_closure,gramic/rules_closure,jart/rules_closure,jart/rules_closure