Bug 1021788 - [Messages] Can't click on the suggestion list when there are a lot of recipients in the recipients panel

- Set fix height for subheader under the new compose view
I just want to share that it was removed in https://github.com/mozilla-b2g/gaia/pull/18088/files#diff-40ff32ff8ddce22c88b864f33e07f312L774

We had `height: 0`, what do you think of using the same rule again so that we don't depend on any magic value?