Avoid setting the SMOL_THREADS environment variable

[notgull]

smol-potat/smol-potat-macro/src/lib.rs

Lines 111 to 114 in 3c819fd

	#crate_root::std::env::set_var(
	"SMOL_THREADS",
	#threads,
	);

This is hacky and potentially unsound. See here.