fix(ngStyle): correctly remove old style when new style value is invalid
Since d6098ee, old styles were not removed if `newStyles` specified an invalid value for the style (e.g. `false`). The assumption was that the new style would overwrite the old style value, but using an invalid value made browsers ignore the new value and thus keep the old style. This would typically happen when guarding a style with a boolean flag; e.g.: `ng-style="{backgroundColor: isError && 'red'}"`
This commit essentially revers commit d6098ee, whose main purpose was to work around jquery/jquery#4185. The jQuery issue has been fixed in 3.4.0, so that should not be a problem any more.