[3.0] Bumped the minimum php version to 5.5

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | yes
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

##### This pull request bumps the minimum php version of symfony 3.0 to php 5.5.

This also removes all the hacky workarounds for php 5.3 and 5.4.
I tought, the default `null` value was a way for the developper to let symfony decide if the parameter should be `true` or `false`. Which only sets it to `true` when the version of php is greater than 5.3.7
And given this is the last parameter of the list, I did not see why someone will explicitly pass null to this method.

BTW, We could keep this behaviours. It will just like weird in few year when someone will read 
```
function foo($param = null) {
  if ($param === null) $param = true;
}
```