remove special handling of @<- and slot<- in replacements

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

...c/com/oracle/truffle/r/nodes/builtin/base/UpdateSlot.java

...oracle/truffle/r/nodes/builtin/fastr/FastRSlotAssign.java

...cle/truffle/r/nodes/builtin/methods/R/methods_overrides.R

...src/com/oracle/truffle/r/nodes/access/UpdateSlotNode.java

...c/com/oracle/truffle/r/nodes/control/ReplacementNode.java

...rc/com/oracle/truffle/r/nodes/unary/GetNonSharedNode.java

...le.r.runtime/src/com/oracle/truffle/r/runtime/RError.java

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