Remove preachy advice from contribution guidelines.

Author: weitzman

CONTRIBUTING.md

@@ -10,8 +10,6 @@ Drush is built by people like you! Please [join us](https://github.com/drush-ops
 ## Coding style
 * Do write comments. You don't have to comment every line, but if you come up with something thats a bit complex/weird, just leave a comment. Bear in mind that you will probably leave the project at some point and that other people will read your code. Undocumented huge amounts of code are nearly worthless!
 * We use [PSR-2](http://www.php-fig.org/psr/psr-2/) in the /src directory. [Drupal's coding standards](https://drupal.org/coding-standards) are still used in the includes directory (deprecated code).
-* Don't overengineer. Don't try to solve any possible problem in one step, but try to solve problems as easy as possible and improve the solution over time!
-* Do generalize sooner or later! (if an old solution, quickly hacked together, poses more problems than it solves today, refactor it!)
 * Keep it compatible. Do not introduce changes to the public API, or configurations too casually. Don't make incompatible changes without good reasons!
 
 ## Documentation