Remove package.json dependencies during build

The kibana app itself requires that package.json exist, so removing it
entirely from distributions is a no go. Instead, we remove only the
dependencies themselves from the package.json so people do not try to
reinstall dependencies on an official distribution.

tasks/build/index.js

@@ -13,6 +13,7 @@ module.exports = function (grunt) {
     '_build:packageJson',
     '_build:readme',
     '_build:installNpmDeps',
+    '_build:removePkgJsonDeps',
     'clean:testsFromModules',
     'clean:deepModuleBins',
     'clean:deepModules',

tasks/build/removePkgJsonDeps.js

@@ -0,0 +1,12 @@
+module.exports = function (grunt) {
+  grunt.registerTask('_build:removePkgJsonDeps', function () {
+    const pkg = grunt.file.readJSON('build/kibana/package.json');
+
+    delete pkg.dependencies;
+
+    grunt.file.write(
+      'build/kibana/package.json',
+      JSON.stringify(pkg, null, '  ')
+    );
+  });
+};