src: clean up experimental flag variables #5511

Job	Run time
Build slim tarball	2m 12s
aarch64-darwin: with shared libraries	23m 1s
aarch64-linux: with shared libraries	21m 56s
x86_64-darwin: with shared libraries	44m 12s
x86_64-linux: with shared libraries	26m 48s
	1h 58m 9s

Provide feedback