Fix: 2094 Enable the ability to clear environment variables

[aldipower]

I should be able to clear the a row by pressing on the "-"-button, if there is only 1 row left, because I maybe want to remove my env vars completely. Of course the row line stays, but empty.

Before:

After pressing on each "-":

Fixes d2iq-archive/marathon#2094

[aldipower]

Should be merged into #158 before.

[philipnrmn]

This behaviour was deliberately introduced in PR #162. It was requested to address some usability issues in the modal: d2iq-archive/marathon#950 (comment)

decrease opacity to 50% on the "(–)" icon when editing the last remaining row of a duplicable set of values (disabled state)

[aldipower]

This behavior prevents the user from removing the last environment variable, so this would stay forever, even if not needed anymore.

[philipnrmn]

I agree it would be nice to be able to clear the last value by using a 'reset' button.

Dimming the ⊖ button but leaving it enabled seems really confusing.

[aldipower]

Yes, so don't dimm.

[philipnrmn]

In that case shouldn't we just revert 9e83115 rather than merging this PR?

[aldipower]

Ok, if you know how to do this, it's the cleaner way.. :)