Cleanup project file.
[REM]: old library references. New libraries are under prebuilt.
[ci skip]
accelerometer fix
Merge pull request #6817 from minggo/accelerometer-fix

[ci skip]accelerometer fix
[Jenkins][ci skip] Add check slave online status to watchdog
Merge pull request #6808 from Mazyod/cleanup-2d-platform

Cleanup 2d/platform library references
Merge pull request #6818 from lmskater/add-watch-slave-offline

[Jenkins][ci skip] Add check slave online status to watchdog
Release Notes for v3.1
Merge pull request #6821 from ricardoquesada/release_notes_3_1

Release Notes for v3.1
Update RELEASE_NOTES.md
Update RELEASE_NOTES.md
Update RELEASE_NOTES.md
Update RELEASE_NOTES.md
Update RELEASE_NOTES.md
[Jenkins][ci skip] A missing import to ci-release-test.py
Merge pull request #6823 from lmskater/add-missing-import

[Jenkins][ci skip] A missing import to ci-release-test.py