BUG 1055363 remove role search of styling of compose form

cf https://bugzilla.mozilla.org/show_bug.cgi?id=1055363
so, these changes are not enough.

* in the same file, there is another rule with `[role="search"]; I think it's useless now that we don't have this attribute, because it especially overrides something set in the building blocks, that we don't use if we remove the attribute. So you can just remove it.
* same thing in sms.css, there is a z-index rule that is useless (I tried removing it and saw no effect)

But there is a bigger problem: the send button is also affected by the change. By inspecting in Firefox on the master branch, you clearly see it has a lot of properties coming from the building blocks for role=search... For this, I wonder if we should create a new class that would be styled in the building blocks instead of copying all properties to the CSS files for SMS. I'll ask someone on the bug.