Remove html5 fork.

The necessary changes were merged upstream to remove the html5 fork.

Relevant commits:

  c64d1d0cce3ce8b55bd69df38dbb778555e30410
  7bd2df748b013d17971427e953b23a53356a982c
  0e287fc08bbb754efa9b9163e7055c1f05d7daca
  0d6c4aaf4e3621d576c7a15a84b243af71af793b
  98aaa4306b0c15c58c21051228a0bb614b860b46

and:

  https://github.com/aredridel/html5/commit/efe3b209643f12038226ef33c030e4e2d20e20ce
  https://github.com/aredridel/html5/commit/18370a4919be4769f99fad4335d323745f51cbd8

Change-Id: I2a3b4d3e67f118ef702a2e9dc2b61c05b27dfaab
Merge "Remove html5 fork."