Removed obsolete delegate connection classes.

.../com/oracle/truffle/r/runtime/conn/ConnectionSupport.java

...om/oracle/truffle/r/runtime/conn/DelegateRConnection.java

...uffle/r/runtime/conn/DelegateReadNonBlockRConnection.java

...racle/truffle/r/runtime/conn/DelegateReadRConnection.java

.../r/runtime/conn/DelegateReadWriteNonBlockRConnection.java

.../truffle/r/runtime/conn/DelegateReadWriteRConnection.java

...ffle/r/runtime/conn/DelegateWriteNonBlockRConnection.java

...acle/truffle/r/runtime/conn/DelegateWriteRConnection.java

...rc/com/oracle/truffle/r/runtime/conn/PipeConnections.java

...m/oracle/truffle/r/test/library/base/TestConnections.java