[analyzer] Don't special-case ivars backing +0 properties.

Give up this checking in order to continue tracking that these values came from
direct ivar access, which will be important in the next commit.

Part of rdar://problem/20335433

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@233591 91177308-0d34-0410-b5e6-96231b3b80d8