configure still allows --disable-rustbuild

[binarycrusader]

As far as I know, it's no longer possible to not use rustbuild, so ./configure offering --disable-rustbuild doesn't make much sense and it still accepts it:

./configure --help|grep rustbuild
    --disable-rustbuild              don't use the rust and cargo based build system

$ ./configure --disable-rustbuild
...
configure: processing ./configure args
configure: 
configure: CFG_DISABLE_RUSTBUILD := 1 
...
configure: configured in release mode. for development consider --enable-debug
configure: 
configure: run `python ./x.py --help`
configure: 
$