Fix a number of flake8 errors

Broadly three things here:

* disable W504 which seems a bit whacko
* remove a bunch of `as e` expressions from exception handlers that don't use
  them
* use `r""` for strings which include backslashes

Also, we don't use pep8 any more, so we can get rid of the duplicate config
there.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/4082.misc b/changelog.d/4082.misc
new file mode 100644
index 0000000000..a81faf5e9b
--- /dev/null
+++ b/changelog.d/4082.misc
@@ -0,0 +1 @@
+Clean up some bits of code which were flagged by the linter