Enable several layout tests again

Several layout test have been disabled because surrogate pair support is not enabled by default on Windows XP En.

Now that we no longer care about Windows XP, we can safely enable those tests.

No behavior change is intended in production binaries.

BUG=none
TEST=unittest


git-svn-id: http://mozc.googlecode.com/svn/trunk@529 a6090854-d499-a067-5803-1114d4e51264