clean up loop nodes (split while and repeat, remove unnecessary functions)

...e.r.nodes/src/com/oracle/truffle/r/nodes/RASTBuilder.java

.../com/oracle/truffle/r/nodes/control/AbstractLoopNode.java

...nodes/src/com/oracle/truffle/r/nodes/control/ForNode.java

...es/src/com/oracle/truffle/r/nodes/control/RepeatNode.java

...des/src/com/oracle/truffle/r/nodes/control/WhileNode.java

...rc/com/oracle/truffle/r/nodes/function/RCallBaseNode.java

...truffle/r/nodes/function/RCallBaseNodeWrapperFactory.java

...es/src/com/oracle/truffle/r/nodes/function/RCallNode.java

...com/oracle/truffle/r/nodes/function/RCallSpecialNode.java

...ntime/src/com/oracle/truffle/r/runtime/data/RPromise.java