[clang] [clang][NFC] Reduce one of JSON dump tests (PR #195026)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

One small example of what I mean is: `git show ba9d1c41c41d568a798e0a8c38a89d294647c28d -- clang/test/AST/ast-dump-templates.cpp`

These kinds of updates to the textual AST dump are really annoying to perform manually. And this is even one of the easy ones, where there is enough context to actually understand what's changing. Most textual AST dump tests lack CHECK-NEXT lines.

I think the point of these tests is to be exhaustive. I don't expect to just be able to read the test files under `clang/test/AST` in isolation and see a small set of things being tested. The value here is seeing what changed under those tests for a given commit.

https://github.com/llvm/llvm-project/pull/195026