[SLICOT] Remove variants of libblastrampoline before build

[vchuravy]

Trying to fix #4969

[RalphAS]

@vchuravy I suspect we should do something like #5622 for now.
@giordano Would that allow us to drop the julia-version variations (i.e. just have the usual platform-gfortran list)?

[giordano]

@giordano Would that allow us to drop the julia-version variations (i.e. just have the usual platform-gfortran list)?

No:

Yggdrasil/S/SLICOT/build_tarballs.jl

Lines 101 to 102 in 18bec01

	# Since we need to link to libblastrampoline which has seen multiple
	# ABI-incompatible versions, we need to expand the julia versions we target