Back out C++11 changes for ICU >= 59

r449608, r449609, r449610, r449611, r449612, r449613, r449614,
r449621, r449661, r449662 are reverted. ICU will pull char16_t typedef
in C++98 mode instead.

Pointy hat to: jbeich
PR: 218788 222222 222225