Fix 'terminal history off' crasher
Fix 'terminal history off' crasher

- 'set terminal history off' or '... limit 0' has an incorrect
  terminal condition and tries to vec_delete one-too-many times
  causing a crash.
- Changing >= to > fixes this.
- In any case, a single vec_delete is more efficient, so do that
  instead.

Change-Id: Ia0db63b6c5c7891d75b302e793b4e4985dd86ebb
Signed-off-by: Chris Luke <77b9dc41542bba50ff94234985ac7feef3984b39@flirble.org>

FDio/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,vpp-dev/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp,FDio/vpp,chrisy/vpp,vpp-dev/vpp