The single externs/olx.js file describes all of the "options" objects we accept in our constructors. The @typedef annotations are used by the compiler for type checking. The @type annotations include documentation for individual options and serve as externs when compiling a profile of the library. When compiling an application together with the library, the externs/olx.js file is included as one of the sources to provide the @typedef's without generating externs.
If we want to maintain multiple src/*.externs.js files instead of one large externs/olx.js file, we can. But while we are still using Plovr, it makes for easier build configurations to have one file.
This removes the build tasks that generated the build/src/external/src/externs/types.js and build/src/internal/src/types.js files as those are both replaced by the single externs/olx.js file.
