Package - remove deprecated $defaultModules from boot()-method.

[Chrico]

Please check if the PR fulfills these requirements

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes/features)
• Docs have been added/updated (for bug fixes/features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

This PR removes the deprecated Module ...$defaultModules in Package::boot().

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.82%. Comparing base (d4ea195) to head (2b1e7b4).
⚠️ Report is 47 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@## master #53 +/- ##
============================================
- Coverage 98.42% 97.82% -0.60% - Complexity 238 308 +70 
============================================
Files 10 10 Lines 570 735 +165 ============================================
+ Hits 561 719 +158 - Misses 9 16 +7 

Flag	Coverage Δ
unittests	97.82% <100.00%> (-0.60%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[gmazzap]

The code is fine, I guess it needs to have a rebase from master, because some of the reported CS issues are already fixed.

But this requires a new major version. I think it would be better to release a minor version with the code from #51 and #52 (when merged) before working on a new major.

[Chrico]

Closed in favor of #60.