Remove SJCL submodule.
Squashed 'src/js/sjcl/' content from commit 28d8573

git-subtree-dir: src/js/sjcl
git-subtree-split: 28d8573235787113fd60daf9d786418695797824
Merge commit '8e54231a6c664154302dd72c4ce935233ae8d8de' as 'src/js/sjcl'