Simplify erl parse precedences

Operator precedences (as [defined here](http://erlang.org/doc/man/yecc.html#id63693)) were used to clarify the recursive grammar rules **expr** and **type**.
Code is now uniform, shorter and I hope, easier to read.
However, [this patch](https://github.com/fenollp/otp/commit/6e8c5cd2fb086451877b246c9c1a77c6ecc61856) added [a shift/reduce conflict](https://github.com/fenollp/otp/commit/e78417900202cc92bc990dcd642309a4289ba1eb).