Before renaming, all Python 2 filenames were 'learnpython-*.py'.
This commit renames them to 'learnpythonlegacy-*.py'.
To verify that the filenames were named consistently across
translations prior to this commit, and to change this:
```
find . -name "pythonlegacy*.markdown" -exec ack filename: {} \;
find . -name "pythonlegacy*.markdown" -exec \
sed -i 's/^filename: learnpython/filename: learnpythonlegacy/' {} \;
```
```
for f in $(find . -iname "*python*" | grep -vE 'python3|git|statcomp'); do
flegacy=$(echo "$f" | sed 's/python/pythonlegacy/')
git mv "$f" "$flegacy"
done
```