don't require libsvm-dev to build

scikit-learn ships a modified LIBSVM. Also removed the patch to use
system LIBSVM, which is not going to work anyway (it wasn't used).

debian/control

@@ -8,7 +8,6 @@ Build-Depends: debhelper (>= 7.0.50), dh-autoreconf,
                cython (>= 0.12~),
                python-setuptools,
                python-numpy, python-scipy,
-               libsvm-dev (>= 2.84.0),
                python-nose,
                python-matplotlib,
                python-joblib (>= 0.4.5), python-support

debian/patches/deb_use_system_libraries

-From: Yaroslav Halchenko <debian@onerussian.com>
-Subject: Use system libraries as specified in site.cfg
-
---- a/site.cfg
-+++ b/site.cfg
-@@ -1,9 +1,9 @@
- 
- # Uncomment to link against system-wide libsvm
--# [libsvm]
--# libraries=svm
--# library_dirs=/usr/lib
--# include_dirs=/usr/include/libsvm-2.0/libsvm
-+[libsvm]
-+libraries=svm
-+library_dirs=/usr/lib
-+include_dirs=/usr/include/libsvm-2.0/libsvm
- 
- # Uncomment to link against the MKL library on windows
- # [mkl]