delete portable-simd/rust-toolchain file #1663

# to view logs

Job	Run time
test-core	5m 45s
test-alloc	30m 4s
test-std	1h 6m 23s
test-simd	1h 19m 24s
test-stdarch	34m 26s
Success	1s
cronjob failure notification	0s
automatic rustup PR	0s
	3h 36m 3s

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