[clang] Enable sized deallocation by default in C++14 onwards

Since C++14 has been released for about nine years and most standard
libraries have implemented sized deallocation functions, it's time to
make this feature default again.

Reviewed By: rnk, aaron.ballman, #libc, ldionne, Mordante, MaskRay

Differential Revision: https://reviews.llvm.org/D112921