androidndkPkgs: separate build and target ndkInfoFun

remove unused hostInfo variable, the uses of it were removed in (androidndk: remove legacy ndks)[2408ef3c6faa0ba0d513257378563ddc886f1020].

This prevents exiting with `error "attribute 'triple' missing"`
It's better to exit with a throw than a attribute missing which cannot

pkgs/development/androidndk-pkgs/androidndk-pkgs.nix

···
   # than we do. We don't just use theirs because ours are less ambiguous and
   # some builds need that clarity.
   #
-  # FIXME:
-  # There's some dragons here. Build host and target concepts are being mixed up.
-  ndkInfoFun = { config, ... }: {
+  ndkBuildInfoFun = { config, ... }: {
     x86_64-apple-darwin = {
       double = "darwin-x86_64";
     };
     x86_64-unknown-linux-gnu = {
       double = "linux-x86_64";
     };
+  }.${config} or
+    (throw "Android NDK doesn't support building on ${config}, as far as we know");
+
+  ndkTargetInfoFun = { config, ... }: {
     i686-unknown-linux-android = {
       triple = "i686-linux-android";
       arch = "x86";
···
       triple = "aarch64-linux-android";
     };
   }.${config} or
-    (throw "Android NDK doesn't support ${config}, as far as we know");
+    (throw "Android NDK doesn't support targetting ${config}, as far as we know");
 
-  buildInfo = ndkInfoFun stdenv.buildPlatform;
-  hostInfo = ndkInfoFun stdenv.hostPlatform;
-  targetInfo = ndkInfoFun stdenv.targetPlatform;
+  buildInfo = ndkBuildInfoFun stdenv.buildPlatform;
+  targetInfo = ndkTargetInfoFun stdenv.targetPlatform;
 
   inherit (stdenv.targetPlatform) sdkVer;
   suffixSalt = lib.replaceStrings ["-" "."] ["_" "_"] stdenv.targetPlatform.config;