Fixed a small bug in the let transformation in which the old let scope was accidentally left in the AST.
Fixed a small bug in the let transformation in which the old let scope
was accidentally left in the AST.

This was caught by a test in verify that I still have commented out.
The test makes sure that all of the symbols in the Symboltable (with
some exceptions) have DefExprs in the AST that is actually traversed.


git-svn-id: 88467cb1fb04b8a755be7e1ee1026be4190196ef@3924 3a8e244f-b0f2-452b-bcba-4c88e055c3ca

CoryMcCartan/chapel,chizarlicious/chapel,CoryMcCartan/chapel,chizarlicious/chapel,sungeunchoi/chapel,CoryMcCartan/chapel,chizarlicious/chapel,CoryMcCartan/chapel,hildeth/chapel,chizarlicious/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,CoryMcCartan/chapel,sungeunchoi/chapel,sungeunchoi/chapel,hildeth/chapel,chizarlicious/chapel,hildeth/chapel,hildeth/chapel,sungeunchoi/chapel,sungeunchoi/chapel,hildeth/chapel,hildeth/chapel,sungeunchoi/chapel,sungeunchoi/chapel,hildeth/chapel,chizarlicious/chapel,sungeunchoi/chapel,chizarlicious/chapel