Ain is in homebrew-core now

Remove my homebrew-tools repo
and use the main homebrew-core
Formulae.

Ain has been in the homebrew-core
for some months now, switch
over the installation
process.

Test plan:
* docker run .it homebrew/brew:latest bash
  brew install ain.
  ain -v.

README.md

@@ -72,7 +72,6 @@ go install github.com/jonaslu/ain/cmd/ain@latest
 ## Via homebrew
 Using the package-manager [homebrew](https://brew.sh)
 ```
-brew tap jonaslu/tools
 brew install ain
 ```