don’t call RBuiltinNode.executeBuiltin from other nodes

...n/src/com/oracle/truffle/r/nodes/builtin/base/Assign.java

...com/oracle/truffle/r/nodes/builtin/base/EnvFunctions.java

...iltin/src/com/oracle/truffle/r/nodes/builtin/base/Gc.java

...com/oracle/truffle/r/nodes/builtin/base/GetFunctions.java

...n/src/com/oracle/truffle/r/nodes/builtin/base/Mapply.java

...m/oracle/truffle/r/nodes/builtin/base/TraceFunctions.java

...ruffle/r/nodes/builtin/base/fastpaths/AssignFastPath.java

...des/builtin/base/system/ContextSystemFunctionFactory.java

...om/oracle/truffle/r/nodes/builtin/fastr/FastRContext.java

.../com/oracle/truffle/r/nodes/builtin/fastr/FastRTrace.java

...oracle/truffle/r/nodes/test/BinaryArithmeticNodeTest.java

...m/oracle/truffle/r/nodes/binary/BinaryArithmeticNode.java