Remove dependency on cvs.

cvs is used to retrieve newlib, which is not supported
under Buildroot, so cvs is not required.

--- crosstool-ng-1.8.0/configure.orig	2010-11-27 15:43:52.000000000 +0000
+++ crosstool-ng-1.8.0/configure	2010-11-27 15:44:10.000000000 +0000
@@ -359,7 +359,6 @@
              err="'libtool' 1.5.26 or above was not found"
 has_or_abort prog=stat
 has_or_abort prog="curl wget"
-has_or_abort prog=cvs
 has_or_abort prog=patch
 has_or_abort prog=tar
 has_or_abort prog=gzip