util-linux: Remove -Werror=format-nonliteral from compiler flags

util-linux uses autogenerated non-literal format strings in its hexdump
code. Those strings have been verified to be safe in 2.35.1.

Removing -Werror=format-nonliteral here allows us to use
-Werror=format-nonliteral globally in OPTIMIZE_FOR=security mode
while keeping util-linux building.

Signed-off-by: Bernhard Rosenkränzer <bernhard.rosenkraenzer.ext@huawei.com>