Revert "Homebrew: Compile as release build."

Reverts neovim/neovim#1366, since asserts are valuable while the project is still in heavy development.

We can use `-Og` for gcc builds to get a reasonably optimized debug builds:

https://github.com/neovim/neovim/pull/1366#issuecomment-61325586

For clang we will just need to deal with it.