[software] Clean up folded MIMO-MMSE and solution of triangular system #1960

Job	Run time
tc-llvm	58s
tc-gcc	25s
riscv-isa-sim	17s
verilator	6s
check-opcodes	4s
verilator-model (minpool)	12s
verilator-model (mempool)	13s
check-bootrom	23s
build-apps-gcc (minpool)	44s
build-apps-gcc (mempool)	34s
unit-test	2m 4s
tc-halide	15s
build-apps-llvm (minpool)	40s
build-apps-llvm (mempool)	40s
run-apps-gcc	0s
build-apps-halide (minpool)	42s
build-apps-halide (mempool)	37s
run-apps-llvm	0s
run-apps-halide (minpool)	18s
run-apps-halide (mempool)	11s
clean-up	3s
clean-up-compile-runs (minpool)	5s
clean-up-compile-runs (mempool)	2s
	9m 33s

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