Revert #7944 as some CI jobs fail

with "unrecognized command line option '-std=gnu17'"

Author: cakebaker

.cargo/config.toml

@@ -1,9 +1,5 @@
-# spell-checker:ignore CFLAGS
-
 [target.x86_64-unknown-redox]
 linker = "x86_64-unknown-redox-gcc"
 
 [env]
 PROJECT_NAME_FOR_VERSION_STRING = "uutils coreutils"
-# TODO remove when there is an onig version > 6.4.0, https://github.com/rust-onig/rust-onig/issues/196
-CFLAGS='-std=gnu17'