Build process updated:

You have to specify `TARGET` to specify a configuration, e.g.

```
rake TARGET=host-debug all test
```

When you port `mruby` to a new configuration:
1. copy an existing configuration under `target` directory
2. modify the new configuration file
3. build using the new configuration
4. send PR if you please

1 files changed, 0 insertions, 26 deletions

diff --git a/examples/targets/build_config_android_arm64-v8a.rb b/examples/targets/build_config_android_arm64-v8a.rb
deleted file mode 100644
index 70b0f4b97..000000000
--- a/examples/targets/build_config_android_arm64-v8a.rb
+++ /dev/null
@@ -1,26 +0,0 @@
-MRuby::Build.new do |conf|
-
-  # Gets set by the VS command prompts.
-  if ENV['VisualStudioVersion'] || ENV['VSINSTALLDIR']
-    toolchain :visualcpp
-  else
-    toolchain :gcc
-  end
-
-  enable_debug
-
-  # include the default GEMs
-  conf.gembox 'default'
-end
-
-# Requires Android NDK r13 or later.
-MRuby::CrossBuild.new('android-arm64-v8a') do |conf|
-  params = {
-    :arch => 'arm64-v8a',
-    :platform => 'android-24',
-    :toolchain => :clang,
-  }
-  toolchain :android, params
-
-  conf.gembox 'default'
-end