Closes https://github.com/llvm/llvm-project/issues/58199
Previously, when we act on a import statement, we'll assume there is a
module declaration in the current TU if the command line tells us we're
compiling a module unit. This makes since on valid codes. However, for
invalid codes, it is possible. See
https://github.com/llvm/llvm-project/issues/58199 for example.
This patch removes the assertion. And the assertion is a noop and it
should be safe to remove it.
Chuanqi Xu