Probably was done to avoid the shadowing issue, but work around it
instead.

Not used, except in tests.

This has been there since as far as the git history goes (2007), is not
covered by any test, and says "Buggy python version consider upgrading".
Hopefully everyone have upgraded...

inspect.getsource() definitely returns str.

It isn't used, so keep it simple.

Cross-type comparisons like this are a bad idea. This isn't used.

eval() is used for evaluating string conditions in skipif/xfail e.g.

    @pytest.mark.skipif("1 == 0")

This is the only code that uses `_pytest._code.compile()`, so removing
its last use enables us to remove it entirely.

In this case it doesn't add much. Plain compile() gives a good enough
error message.

For regular exceptions, the message is the same.

For SyntaxError exceptions, e.g. "1 ==", the previous code adds a little
bit of useful context:

```
invalid syntax (skipping.py:108>, line 1)

The above exception was the direct cause of the following exception:
1 ==
     ^
(code was compiled probably from here: <0-codegen /pytest/src/_pytest/skipping.py:108>) (line 1)

During handling of the above exception, another exception occurred:
Error evaluating 'skipif' condition
    1 ==
         ^
SyntaxError: invalid syntax
```

The new code loses it:

```
unexpected EOF while parsing (<skipif condition>, line 1)

During handling of the above exception, another exception occurred:
Error evaluating 'skipif' condition
    1 ==
        ^
SyntaxError: invalid syntax
```

Since the old message is a minor improvement to an unlikely error
condition in a deprecated feature, I think it is not worth all the code
that it requires.

A lot of complex code that isn't used anymore outside of tests after
the previous commit.

The recursive way in which Source and getsource interact is a bit
confusing, just inline it.