Fix inset link buttons not looking like buttons

[joshhanley]

Currently if we have a button that is inset and another button that has a href and is inset, they do not look the same.

<div class="mt-4 space-y-4">
    <flux:button variant="ghost" inset>Button with inset</flux:button>
    <flux:button variant="ghost" inset href="#">Button with inset and href</flux:button>
</div>

This was previously fixed in PR #35 for links, but the issue now happens for link-buttons that use the inset prop.

The reason this happens is in the code for the button, there is this line and comment ->add($inset ? 'flex' : 'inline-flex') // inline-flex is weird with negative margins....

The inline-flex was added in PR livewire/flux#35 to ensure that link-buttons looked like standard buttons. This was because buttons are inline-block by default and links are block by default, so inline-flex needed to be applied so they get treaded the same way.

So for link-buttons to work with inset, we need to re-enable the inline-flex for inset buttons and link-buttons.

I've done some testing with buttons and link buttons both set to flex and inline-flex, to see if I could work out how inline-flex and negative margins could interact, and I couldn't see any differences.

As I can't work out exactly what weird negative margin issues inline-flex required that line of code to be added, I think we should just remove it for now and see if we can any bug reports regarding it.

So this PR removes that line.

Fixes #801