Remove macOS dependency

[dmasiero]

See issue #422 and homebrew issue 58046

[CLAassistant]

All committers have signed the CLA.

[petems]

For people googling this (like I ended up doing) this is the fix for the following:

==> Tapping puppetlabs/puppet
     Cloning into '/opt/homebrew/Library/Taps/puppetlabs/homebrew-puppet'...
     Tapped 13 casks and 9 formulae (52 files, 1.7MB).
     Error: Calling `depends_on macos: :el_capitan` is disabled! There is no replacement.
     Please report this issue to the puppetlabs/homebrew-puppet tap (not Homebrew/* repositories):
       /opt/homebrew/Library/Taps/puppetlabs/homebrew-puppet/Casks/puppet-bolt.rb:71

Can someone at Puppet look into this for a fix?