ci: travis: osx: switch to newer macos image and brew addon for packages

ci: travis: osx: switch to newer macos image and brew addon for packages

Summary:
One of the time consuming parts of the macos build we have is the
installing of the efl dependencies as packages from brew.
The brew update command alone is often taking 5m to run.

To avoid running brew update at all we are switching to a newer osx
image from Travis, which comes with a newer set of brew metadata and
gets us around a brew update for now. Together with this we are also
switching from our own dependency install script to the brew package
addon provided by travis already.

In my testing this shows we are only spending 270s in the brew package
updates comapred to 635s before. So we have a 6 minutes speedup for
every osx build!
Depends on D9161

Reviewers: zmike, bu5hm4n

Reviewed By: zmike

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D9162