Suite Sparse: refactor formula.

Several make variables are defined multiple times in
SuiteSparse_config_Mac.mk and sometimes with leading blanks. This caused
change_make_var to only change some of them and led to a bug where
SuiteSparse uses Accelerate even if the user selects OpenBLAS.

This update removes change_make_var entirely. See also:
https://github.com/Homebrew/homebrew/pull/27483