Allow clippy::disallowed_names since it can be used for debugging

https://rust-lang.github.io/rust-clippy/master/index.html#/disallowed_names

The current list is extremely short ("foo", "baz", "quux"), and thus
this really just prevents people from temporarily using `foo` to debug
code. In the spirit of improving productivity and reducing frustration,
it's easier to just allow this.

Bug: N/A
Test: TH
Change-Id: I50b65486ed2b58bfd2cf699ee3b43b936d25f2cb