[clang] [NFC][analyzer] Remove the NodeBuilder from eagerly assume (PR #204371)

[Balázs Benics via cfe-commits]

steakhal wrote:

When asked some AI to confirm that this is NFC, it told me that there might be an issue:

Previously, when both `StateTrue` and `StateFalse` were `null` (the symbolic condition is unsatisfiable in the current state), `Pred` remained in the Frontier/Dst because `NodeBuilder::generateNode` was never called and could never erase it. With this patch, that path is dropped: no `Dst.insert(Pred)` runs.

I'm not sure, but AFAIK `StateTrue` and `StateFalse` could be null at the same time, so this sounds plausible to me.

https://github.com/llvm/llvm-project/pull/204371