PR30734: Remove __kmp_ft_page_allocate()

This function was not enabled by default and not exported when manually
tweaking the build flags. Additionally it was hard to use since there
is no corresponding __kmp_ft_page_free().
The code itself is questionable because the returned memory address
is padded by an extra pointer which stores the unpadded start of the
allocated region (this would need to be freed).

Differential Revision: https://reviews.llvm.org/D49802

llvm-svn: 338052