debian: libltdl-dev version no more needed

Warning in 'control source Build-Depends:4': unnecessary greater-than versioned dependency: libltdl-dev (>= 2.2.6b). Debian has oldoldstable -> 2.4.2-1.11; oldoldstable -> 2.4.2-1.11+b1; oldstable -> 2.4.6-2; stable -> 2.4.6-9; testing -> 2.4.6-14; unstable -> 2.4.6-14;

Signed-off-by: Philippe Coval <rzr@users.sf.net>
Change-Id: Ia613efcad3e1d4d514a55f1875bafd1c1a71e0ed