Simplify the google-map example

By creating the ol3 map div in the html, there is no need any
more to wait for the custom GMaps control to append the ol3 map
to its parent. This also fixes an issue that sometimes prevented
the ol3 map to appear, when the GMaps tiles were loaded before
the custom control's div was appended to its parent.
Merge pull request #1790 from ahocevar/simpliy-google-example

Simplify the google-map example