Remove `log_function` and its uses (#11761)

I've never found this terribly useful. I think it was added in the early days
of Synapse, without much thought as to what would actually be useful to log,
and has just been cargo-culted ever since.

Rather, it tends to clutter up debug logs with useless information.

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/11761.misc b/changelog.d/11761.misc
new file mode 100644
index 0000000000..d4d997a7b9
--- /dev/null
+++ b/changelog.d/11761.misc
@@ -0,0 +1 @@
+Remove `log_function` utility function and its uses.