[Parse] Remove TimeTraceScope for "ParseTemplate"

Fix https://github.com/llvm/llvm-project/issues/56554

```
#include "1.h"
#include "2.h"
int foo();
```

Suppose that 1.h ends with a template function. When parsing the function,
the `ParseFunctionDefinition` call after the TimeTraceScope object
may consume a `r_brace` token and lex the end of file (1.h), resulting
in an ExitFile event in SemaPPCallbacks::FileChanged. This event will call `llvm::timeTraceProfilerEnd();`,
which incorrectly ends "ParseTemplate" instead of "Source" (1.h).
Once 2.h has been fully parsed, the destructor of 1.h's TimeTraceScope object
will end "Source" (1.h).

This behavior erroneously extends the end of "Source" (1.h), which makes
"Source" (2.h) appear to be nested inside "Source" (1.h). This bug is difficult
to fix correctly in an elegant way, and we have two options: either end
"ParseTemplate" when ending "Source" (1.h), or delay the ExitFile event.

However, both approaches require complex code. For now, we can remove the
"ParseTemplate" TimeTraceScope. This can be re-added if properly repaired.

Reviewed By: anton-afanasyev

Differential Revision: https://reviews.llvm.org/D148410