lib.replaceChars: warn about being a deprecated alias

replaceStrings has been in nix since 2015(nix 1.10)

so it is safe to remove the fallback

https://github.com/nixos/nix/commit/d6d5885c1567454754a0d260521bafa0bd5e7fdb

pkgs/development/mobile/xcodeenv/build-app.nix

@@ -53,7 +53,7 @@ let
   extraArgs = removeAttrs args ([ "name" "scheme" "xcodeFlags" "release" "certificateFile" "certificatePassword" "provisioningProfile" "signMethod" "generateIPA" "generateXCArchive" "enableWirelessDistribution" "installURL" "bundleId" "version" ] ++ builtins.attrNames xcodewrapperFormalArgs);
 in
 stdenv.mkDerivation ({
-  name = lib.replaceChars [" "] [""] name; # iOS app names can contain spaces, but in the Nix store this is not allowed
+  name = lib.replaceStrings [" "] [""] name; # iOS app names can contain spaces, but in the Nix store this is not allowed
   buildPhase = ''
     # Be sure that the Xcode wrapper has priority over everything else.
     # When using buildInputs this does not seem to be the case.

pkgs/development/mobile/xcodeenv/simulate-app.nix

@@ -9,7 +9,7 @@ let
   xcodewrapper = composeXcodeWrapper xcodewrapperArgs;
 in
 stdenv.mkDerivation {
-  name = lib.replaceChars [" "] [""] name;
+  name = lib.replaceStrings [" "] [""] name;
   buildCommand = ''
     mkdir -p $out/bin
     cat > $out/bin/run-test-simulator << "EOF"