toolchain: drop BR2_CROSS_TOOLCHAIN_TARGET_UTILS option

It's really not very useful, all it does is install a target
strace and ldd in a target_utils directory in staging.
While at it clean up the strace makefile a bit.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>