Removed styling in softDropDownButton that causes dark highlighting
Removed styling in softDropDownButton that causes dark highlighting

In the developers tools most of the icons in the listed screens
are completely merged in black colour or not displaying properly.
We have removed the code causing this problem.

Note: this does not fix the darkened out add shortcut button

Bug: 1240558
Change-Id: I49a6db81c44b18233d701eb0d1e1559002867c65
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/3103229
Commit-Queue: Kriti Sapra <1c59404b87eeb378020e678403b339de83991e1f@google.com>
Reviewed-by: Jack Franklin <993fcadce4d04090da2fefd557a0995e7966c8d5@chromium.org>

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