style(Angular.js): remove redundant `_angular`

Going through the commit history on GitHub, the `_angular` is for noConflict mode,
the case where you have an old reference to a variable called Angular you want to preserve.

Here is the commit that added _angular in : https://github.com/angular/angular.js/commit/
12ba6cec4fb79521101744e02a7e09f9fbb591c4

This feature was later removed here:
https://github.com/angular/angular.js/commit/9faabd1ba0b1929785bcf166dc0ff60008e7c442

The variable 'made it through', it's redundant now.

Closes #7215