[NFC][TSan] Allocate ScopedReport as a stack variable (#228637)
Now that ScopedReport is constructed before acquiring ThreadRegistryLock
or slot locks across all reporting functions (#228614), it no longer
needs to be constructed inside the lock scope via placement new on
__builtin_alloca storage (introduced in #151495).
Declare ScopedReport as a normal stack variable before the lock scope
and remove the manual destructor calls.
Assisted-by: Gemini