Revert "Parser: Fix handling of NULL target operands."

This reverts commit b5513899b2931631456f61f5152279d4d505d988.
Change was seen to cause problems under ASLTS test suite.
Revert "Add support for method invocation as a target operand for ASL operators."

This reverts commit f2fd7294de5b93a778160064f6d61df1792f0d0f.
Change was seen to cause problems with the ASLTS test suite and
will need to be reworked/readdressed.