i586_unknown_netbsd.rs: drop "-m32" flag insertion to gcc.

This triggers a consistency check in rust (that all linker flavours
must have identical arguments), and on NetBSD/i386, the 32-bitness
is implicitly chosen through the chosen toolchain, and appears to
not be required.  So drop it, and also drop the imports of the
now-no-longer-used identifiers.

compiler/rustc_target/src/spec/i586_unknown_netbsd.rs

@@ -1,10 +1,9 @@
-use crate::spec::{Cc, LinkerFlavor, Lld, StackProbeType, Target, TargetOptions};
+use crate::spec::{StackProbeType, Target, TargetOptions};
 
 pub fn target() -> Target {
     let mut base = super::netbsd_base::opts();
     base.cpu = "pentium".into();
     base.max_atomic_width = Some(64);
-    base.pre_link_args.entry(LinkerFlavor::Gnu(Cc::Yes, Lld::No)).or_default().push("-m32".into());
     base.stack_probes = StackProbeType::Call;
 
     Target {