[software] Clean up folded MIMO-MMSE and solution of triangular system #2000

Job	Run time
tc-gcc	26s
verilator	6s
riscv-isa-sim	8s
check-opcodes	6s
tc-llvm	57s
verilator-model (minpool)	14s
verilator-model (mempool)	13s
check-bootrom	9s
build-apps-gcc (minpool)	21s
build-apps-gcc (mempool)	28s
unit-test	2m 19s
tc-halide	9s
build-apps-llvm (minpool)	36s
build-apps-llvm (mempool)	34s
run-apps-gcc	0s
build-apps-halide (minpool)	47s
build-apps-halide (mempool)	1m 14s
run-apps-llvm	0s
run-apps-halide (minpool)	11s
run-apps-halide (mempool)	14s
clean-up	4s
clean-up-compile-runs (minpool)	3s
clean-up-compile-runs (mempool)	6s
	9m 25s

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