function getWebGLContext(canvas, opt_attribs) {
  var gl = create3DContext(canvas, opt_attribs);
  return gl;
}
Gets a WebGL1 context.

Note: Will attempt to enable Vertex Array Objects
and add WebGL2 entry points. (unless you first set defaults with
`twgl.setDefaults({enableVertexArrayObjects: false})`;

@param {HTMLCanvasElement} canvas a canvas element.
@param {WebGLContextAttributes} [opt_attribs] optional webgl context creation attributes
@return {WebGLRenderingContext} The created context.
@memberOf module:twgl
@deprecated
@private