debug/gdb: remove insight

Insight seems to be very slow to follow up on mainstreram gdb.
Latest snapshots are more than 6 months old.

Moreover, I don't have time to maintain insight support in crosstool-NG;
and, because I don't use it, I am unable to find any breakage.

 reporter_name="Bart vd. Meulen"

 reporter_url=""

 reporter_comment="Sample for building a canadian cross-compiler"