Duplicate autogen.sh entry in commoncode default ignores

### Description

`src/commoncode/ignore.py` lists the same key twice in the default ignores, on two byte-identical consecutive lines (204-205):

```python
"autogen.sh": "Default ignore: autotools artifact",
"autogen.sh": "Default ignore: autotools artifact",
```

Nothing misbehaves here — the key and the value are identical, so the dict ends up the same either way. It is just a dead line, and filing it as a small cleanup rather than a bug.

### How To Reproduce

```
$ grep -n '"autogen.sh"' src/commoncode/ignore.py
204: "autogen.sh": "Default ignore: autotools artifact",
205: "autogen.sh": "Default ignore: autotools artifact",
```

```python
import ast, collections

src = open('src/commoncode/ignore.py').read()
for node in ast.walk(ast.parse(src)):
if isinstance(node, ast.Dict):
counts = collections.Counter(
k.value for k in node.keys
if isinstance(k, ast.Constant) and isinstance(k.value, str)
)
for key, n in counts.items():
if n > 1:
print(f'line {node.lineno}: duplicate key {key!r} x{n}')
```

```
line 185: duplicate key 'autogen.sh' x2
```

### Suggested fix

Delete one of the two lines. PR attached.

### System configuration

* What OS are you running on? Linux (x86_64)
* What version of scancode-toolkit was used? 33.0.0rc1, `develop` at 5ebebf2
* What installation method was used to install/run scancode? source checkout
* Python version: 3.x