minor symfony#22104 [WebProfilerBundle] Remove uneeded directive in the form collector (romain-pierre)

This PR was submitted for the master branch but it was merged into the 2.8 branch instead (closes symfony#22104).

Discussion
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[WebProfilerBundle] Remove uneeded directive in the form collector

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | none

Hi, as discussed with @javiereguiluz in symfony#22102, it's better to completely remove this directive to avoid side effects on different Symfony versions. I can see an icon offset on 3.3. This directive was not "present" for so many time.. so...

Commits
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40a67c9 [WebProfilerBundle] Remove uneeded directive in the form collector styles

Author: fabpot

src/Symfony/Bundle/WebProfilerBundle/Resources/views/Collector/form.html.twig

@@ -60,7 +60,6 @@
         }
         #tree-menu .empty {
             border: 0;
-            margin: 0;
             padding: 0;
         }
         #tree-details-container {