Remove grunt and bower global dependencies

We keep having problems with people choosing to intuitively build jQuery instead of following instructions – 
https://github.com/jquery/jquery/pull/1364, https://github.com/jquery/jquery/pull/1391.

Easy solution for it is to remove <code>grunt-cli</code> and <code>bower</code> packages from global dependencies and use them as local ones. Both readme of these packages recommend to install them globally, but it does not mean they would not work if installed locally (actually, it would be strange if they would not work this way). 

As jQuery developer you would still have an option to build jQuery with <code>bower</code> and <code>grunt</code> commands, but with this commit, you would not require to do so. It also simplifies build instructions and might help with dilemma of whether or not put bower components in the repository.