Fixed a bug when removing useless this expressions in anonymous classes.

SimplifyExpressionRefactoring.java:
Moved thisExpressionRefersToSurroundingType() methods from ASTHelper class.

SimplifyExpressionSample.java:
Added tests.

ASTHelper.java:
Added bodyDeclarations().
Moved thisExpressionRefersToSurroundingType() methods to SimplifyExpressionRefactoring class.