remove Function::coeffs_for_jun #1921

Job	Run time
macos-latest: clang++ Release Threads	7m 42s
macos-latest: clang++ Release OneTBB	1m 21s
macos-latest: clang++ Release PaRSEC	1m 35s
ubuntu-20.04: /usr/bin/g++-9 Release Threads	22m 59s
ubuntu-20.04: /usr/bin/g++-9 Release OneTBB	1m 41s
ubuntu-20.04: /usr/bin/g++-9 Release PaRSEC	1m 52s
macos-latest: clang++ Debug Threads	18m 22s
macos-latest: clang++ Debug OneTBB	2m 0s
macos-latest: clang++ Debug PaRSEC	2m 28s
ubuntu-20.04: /usr/bin/g++-9 Debug Threads	48m 7s
ubuntu-20.04: /usr/bin/g++-9 Debug OneTBB	1m 49s
ubuntu-20.04: /usr/bin/g++-9 Debug PaRSEC	1m 56s
	1h 51m 52s

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