backends/xcode: simplify an obviously too-complicated function

This function has a pretty unique name, and a simple grep shows that it
is only ever called as:
```
add_comment(PbxComment('...........'))
```

It doesn't need to include logic such as handling str. Moreover it looks
like that handling was broken anyway... it handled the case where
comment is type str, by constructing a new PbxComment(str) instead of
PbxComment(comment), a condition that cannot ever be valid (and crashed
due to other assertions).

Fixes:

mesonbuild/backend/xcodebackend.py:148:42: error: Argument 1 to "PbxComment" has incompatible type "type[str]"; expected "str"  [arg-type]

0 files changed, 0 insertions, 0 deletions