Auto merge of #3668 - phansch:remove_bors_toml, r=flip1995
Auto merge of #3668 - phansch:remove_bors_toml, r=flip1995

Remove bors.toml

This file was only needed for bors-ng, but now we use the default
rust-lang bors fork.

graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,aidancully/rust