don't declare implicitly exported functions public #3892

Job	Run time
downgrade	1h 28m 53s
test (1.10, ubuntu-latest, core_layers)	18m 58s
test (1.10, ubuntu-latest, normalize_layers)	19m 52s
test (1.10, ubuntu-latest, recurrent_layers)	28m 48s
test (1.10, ubuntu-latest, autodiff)	47m 47s
test (1.10, ubuntu-latest, misc)	28m 20s
test (1.10, ubuntu-latest, reactant)	13m 36s
test (1, ubuntu-latest, core_layers)	23m 58s
test (1, ubuntu-latest, normalize_layers)	23m 40s
test (1, ubuntu-latest, recurrent_layers)	35m 26s
test (1, ubuntu-latest, autodiff)	35m 19s
test (1, ubuntu-latest, misc)	39m 51s
test (1, ubuntu-latest, reactant)	12m 14s
test (1, macos-latest, all)	5h 54m 30s
test (1, windows-latest, all)	1h 36m 19s
	14h 27m 31s

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