Removed fastr.context aliases, modify affected files

com.oracle.truffle.r.native/library/parallel/RSHAREDnode.R

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

...test/src/com/oracle/truffle/r/test/channels/R/channels2.R

...test/src/com/oracle/truffle/r/test/channels/R/channels3.R

...test/src/com/oracle/truffle/r/test/channels/R/channels4.R

...test/src/com/oracle/truffle/r/test/channels/R/channels5.R

...test/src/com/oracle/truffle/r/test/channels/R/channels6.R

...test/src/com/oracle/truffle/r/test/channels/R/channels7.R

...test/src/com/oracle/truffle/r/test/channels/R/channels8.R

...test/src/com/oracle/truffle/r/test/channels/R/channels9.R