minor symfony#28683 Remove redundant path check (colinodell)

This PR was merged into the 2.8 branch.

Discussion
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Remove redundant path check

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | maybe?
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Commit 0ec852d introduced this new method. As you can see, the code I'm removing always evaluates to `true` thanks to the first `if` statement in this method:

![image](https://user-images.githubusercontent.com/202034/46349212-70968a80-c61f-11e8-8360-7d6abc4d7414.png)

(I'm not sure if redundant code technically counts as a "bug", so I've assumed "yes it does" and targeted 2.8.)

Commits
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10795cf Remove redundant path check

Author: fabpot

src/Symfony/Component/HttpFoundation/Request.php

@@ -1120,7 +1120,7 @@ public function getRelativeUriForPath($path)
         }
 
         $sourceDirs = explode('/', isset($basePath[0]) && '/' === $basePath[0] ? substr($basePath, 1) : $basePath);
-        $targetDirs = explode('/', isset($path[0]) && '/' === $path[0] ? substr($path, 1) : $path);
+        $targetDirs = explode('/', substr($path, 1));
         array_pop($sourceDirs);
         $targetFile = array_pop($targetDirs);