Make headers GPL compliant and removed pkginfo #399

Job	Run time
Build MDANSE and run tests on ubuntu-20.04	2m 58s
Build MDANSE and run tests on ubuntu-20.04	2m 54s
Build MDANSE and run tests on ubuntu-20.04	2m 42s
Build MDANSE and run tests on ubuntu-20.04	3m 20s
Build MDANSE and run tests on windows-2019	3m 29s
Build MDANSE and run tests on windows-2019	3m 36s
Build MDANSE and run tests on windows-2019	3m 44s
Build MDANSE and run tests on windows-2019	3m 28s
Build MDANSE and run tests on macOS-11	5m 40s
Build MDANSE and run tests on macOS-11	5m 44s
Build MDANSE and run tests on macOS-11	13m 48s
Build MDANSE and run tests on macOS-11	6m 7s
	57m 30s

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