[analyzer] Drastically simplify the tblgen files used for checkers

Interestingly, only about the quarter of the emitter file is used, the DescFile
entry hasn't ever been touched [1], and the entire concept of groups is a
mystery, so I removed them.

[1] http://lists.llvm.org/pipermail/cfe-dev/2018-October/059664.html

Differential Revision: https://reviews.llvm.org/D53995

llvm-svn: 346680