Bug 987445 - [B2G][SMS]Delete button behavior intermittently unexpected when no conversations are selected r=arnau

This removes the 'vertical-align: middle' property for icon buttons.
Merge pull request #17722 from julienw/987445-v1.3-remove-vertical-align-middle-for-icon-buttons

Bug 987445 - [B2G][SMS]Delete button behavior intermittently unexpected ...