rustdoc: remove no-op CSS `.main-header { justify-content }`

This rule was added in 152e8889052adaaa6c12652486292be34059713c to push the
out-of-band content to the right while allowing it to line wrap when it got
too big. The idea was that the justification rule would fill the space
between the `<h1>` element and the `<div class="out-of-band">` element.

A later commit, 3cb03cb34247383ffb67a017ae70134741e8c4da, flattened the
in-band element into the `<h1>`, copying the `flex-grow` rule. This means
the `<h1>` element now grows to fill the space, so there's no need to
justify-content any more.

This commit also adds a test case for this.

0 files changed, 0 insertions, 0 deletions