docs(guide/compiler): remove innacurate statement
docs(guide/compiler): remove innacurate statement

The $compile service accepts string as a value and wraps it if
needed, so this statement isn't correct, at least by the source
code.

Closes #6301

ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js,ggershoni/angular.js