A small bug fix for `input_defined` variable used in `setup.py`.
I think the only case for downloading shall satisfy all following
requirements:
1. `is_offline_build()` is False
2. `input_defined = p.syspath_var_name in os.environ` is False, which
means using the cache dir.
3. `input_compatible` is False, which means the current cached version
is not correct.
However, the current codes have following issues:
1. `input_defined = p.syspath_var_name not in os.environ`, which is not
consistent with the variable name.
2. When `p.syspath_var_name in os.environ` and version is correct in
that path, it still downloads.
The bug is introduced in commit
triton-lang@ 0503565 
Codes with bug after
triton-lang@ 0503565 :
```python3
        input_defined = p.syspath_var_name not in os.environ
        input_exists = input_defined and os.path.exists(version_file_path)
        input_compatible = input_exists and Path(version_file_path).read_text() == p.url
        if is_offline_build() and not input_defined:
            raise RuntimeError(f"Requested an offline build but {p.syspath_var_name} is not set")
        if not is_offline_build() and not input_compatible:
            with contextlib.suppress(Exception):
                shutil.rmtree(package_root_dir)
```
Old codes without bug before
triton-lang@ 0503565 :
```python3
        if p.syspath_var_name not in os.environ and\
           (not os.path.exists(version_file_path) or Path(version_file_path).read_text() != p.url):
            with contextlib.suppress(Exception):
                shutil.rmtree(package_root_dir)
```
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