refactor(document): remove async.each() dependencies

Re: #8073

lib/helpers/each.js

@@ -0,0 +1,25 @@
+'use strict';
+
+module.exports = function each(arr, cb, done) {
+  if (arr.length === 0) {
+    return done();
+  }
+
+  let remaining = arr.length;
+  let err = null;
+  for (const v of arr) {
+    cb(v, function(_err) {
+      if (err != null) {
+        return;
+      }
+      if (_err != null) {
+        err = _err;
+        return done(err);
+      }
+
+      if (--remaining <= 0) {
+        return done();
+      }
+    });
+  }
+};

lib/plugins/removeSubdocs.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const each = require('async/each');
+const each = require('../helpers/each');
 
 /*!
  * ignore
@@ -17,15 +17,8 @@ module.exports = function(schema) {
     const _this = this;
     const subdocs = this.$__getAllSubdocs();
 
-    if (!subdocs.length) {
-      next();
-      return;
-    }
-
     each(subdocs, function(subdoc, cb) {
-      subdoc.$__remove(function(err) {
-        cb(err);
-      });
+      subdoc.$__remove(cb);
     }, function(error) {
       if (error) {
         return _this.schema.s.hooks.execPost('remove:error', _this, [_this], { error: error }, function(error) {

lib/plugins/saveSubdocs.js

@@ -1,6 +1,6 @@
 'use strict';
 
-const each = require('async/each');
+const each = require('../helpers/each');
 
 /*!
  * ignore

test/document.test.js

@@ -7903,7 +7903,7 @@ describe('document', function() {
         }
       }
     });
-    
+
     const schema = new Schema({
       items: [itemArray]
     });