Remove require-dev section, composer doesn't handle it well

Any "composer require <module>" call will first call
a "composer update". This *automatically* includes dev requirements,
without providing a way to turn off this behaviour.
A workaround would be "composer require --no-update <module> && composer update --no-dev <module>",
but that drastically reduces the usefulness of the command
for our target audience (moderately technical devs).

In the end, the small faction of devs needing the dev dependencies
also know how to install them on their own. And having a local phpunit
build actually gets in the way more than it helps in case you have
it installed through PEAR already (can get really weird when using the
PEAR provided "phpunit" binary, but the autoloader finds the composer managed classes).

composer.json

@@ -7,12 +7,6 @@
 		"silverstripe/framework": "3.0.*@stable",
 		"silverstripe-themes/simple": "*"
 	},
-	"require-dev": {
-		"silverstripe/docsviewer": "*",
-		"silverstripe/behat-extension": "*",
-		"silverstripe/buildtools": "*",
-		"phpunit/phpunit": "3.7.*"
-	},
 	"config": {
 		"process-timeout": 600	
 	},