bootstrap: Remove helpers for upgrading directly from pre 4.4

bootstrap: Remove helpers for upgrading directly from pre 4.4

This is partly needed to smooth out transition between c++98 to c++14
without switching to a rapid release cycling.

Many changes went in since 4.0 involving btools:
gnu/usr.bin/cc50/cc_tools - iconv() c++ issue, pre 4.4
gnu/usr.bin/grep - max_align_t issue, pre 4.2
usr.bin/chflags - chflagsat(2), pre 4.2
usr.bin/gencat - locales, pre 3.6(4.1 for safety)
usr.bin/sort - isnan(), pre 4.4

It is highly recomended to take an intermediate update step to any of
4.4, 4.6, 4.8 or 5.0 releases first when upgrading from older releases.