setup-hooks/strip.sh: redirect stdout to dev/null

to not unnecessarily print

```
hello> ++ type -f strip
hello> strip is /nix/store/xzqzq99kbbkad23s2bf4bbrjppg6x0vj-bootstrap-stage2-gcc-wrapper-/bin/strip
```

printing what the strip command is is already done in stripDirs

`echo "stripping (with command $cmd and flags $stripFlags) in $paths"`

pkgs/build-support/setup-hooks/strip.sh

@@ -36,7 +36,7 @@ _doStrip() {
         local -n ranlibCmd="${ranlibCmds[$i]}"
 
         # `dontStrip` disables them all
-        if [[ "${dontStrip-}" || "${flag-}" ]] || ! type -f "${stripCmd-}" 2>/dev/null
+        if [[ "${dontStrip-}" || "${flag-}" ]] || ! type -f "${stripCmd-}" 2>/dev/null 1>&2
         then continue; fi
 
         stripDirs "$stripCmd" "$ranlibCmd" "$debugDirList" "${stripDebugFlags[*]:--S}"