[GR-2738] Cleanup warnings.

ci.hocon

...fle.r.engine/src/com/oracle/truffle/r/engine/REngine.java

...rc/com/oracle/truffle/r/engine/RRuntimeASTAccessImpl.java

...src/com/oracle/truffle/r/engine/TruffleRLanguageImpl.java

...ngine/src/com/oracle/truffle/r/engine/interop/ListMR.java

...ruffle/r/engine/interop/RAbstractVectorAccessFactory.java

...racle/truffle/r/engine/interop/RArgsValuesAndNamesMR.java

...c/com/oracle/truffle/r/engine/interop/REnvironmentMR.java

.../src/com/oracle/truffle/r/engine/interop/RLanguageMR.java

...e/src/com/oracle/truffle/r/engine/interop/RPromiseMR.java

...ngine/src/com/oracle/truffle/r/engine/interop/RRawMR.java

.../src/com/oracle/truffle/r/engine/interop/RS4ObjectMR.java

...oracle/truffle/r/engine/shell/EmbeddedConsoleHandler.java

...gine/src/com/oracle/truffle/r/engine/shell/REmbedded.java

...src/com/oracle/truffle/r/ffi/codegen/FFITestsCodeGen.java

...l/src/com/oracle/truffle/r/ffi/impl/common/RFFIUtils.java

.../com/oracle/truffle/r/ffi/impl/llvm/TruffleLLVM_Call.java

...ffle/r/ffi/impl/llvm/TruffleLLVM_DownCallNodeFactory.java

...uffle/r/ffi/impl/managed/Managed_DownCallNodeFactory.java

...rc/com/oracle/truffle/r/ffi/impl/nfi/TruffleNFI_Call.java