Revert "Java 11 support (#609)" to fix build

[demirkayaender]

Sending just to try if this was the cause for the build failures.

[coveralls]

Pull Request Test Coverage Report for Build 802

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.009%) to 71.396%

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Files with Coverage Reduction	New Missed Lines	%
src/main/java/com/uber/cadence/internal/sync/WorkflowThreadContext.java	1	82.46%

Totals
Change from base Build 764:	-0.009%
Covered Lines:	10663
Relevant Lines:	14935

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💛 - Coveralls

[demirkayaender]

It's fixed here: #625