DevTools: clean up styles in inspect.css

Removed some overcomplicated styles that accumulated after recent fixes.

BUG=None

Review URL: https://codereview.chromium.org/35183002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230356 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230356