nmap: use system liblinear

nmap: use system liblinear

Use system liblinear instead of using included liblinear.
liblinear in buildroot is at version 2.20 released on December 2017
whereas liblinear in nmap has not been updated since 7 years (except for
liblinear.vcxproj which has been updated 2 years ago)

Do not use --with-liblinear option as otherwise nmap will forget to add
-llinear to LIBS due to the following line in configure.ac:

if test $have_liblinear != yes; then
  AC_CHECK_HEADERS([linear.h],
    AC_CHECK_LIB(linear, predict, [have_liblinear=yes; LIBLINEAR_LIBS="-llinear"; break],, [-lm])
)

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>