Prevent C linkage errors due to templates in extern "C" blocks:
* /usr/lib/gcc/x86_64-pc-linux-gnu/5.3.0/include/g++-v5/bits/cpp_type_traits.h:85:3: error: template with C linkage
*    template<bool>
*    ^
* /usr/lib/gcc/x86_64-pc-linux-gnu/5.3.0/include/g++-v5/bits/cpp_type_traits.h:89:3: error: template specialization with C linkage
*    template<>
*    ^
extern "C" blocks can be removed in shogun, as R internally correctly protects C symbols

--- shogun-4.1.0/src/interfaces/r_modular/sg_print_functions.cpp
+++ shogun-4.1.0/src/interfaces/r_modular/sg_print_functions.cpp
@@ -1,4 +1,3 @@
-extern "C" {
 #include <R.h>
 #include <Rinternals.h>
 #include <Rdefines.h>
@@ -7,7 +6,6 @@
 #include <Rinterface.h>
 #include <R_ext/RS.h>
 #include <R_ext/Error.h>
-}
 
 #include <shogun/base/SGObject.h>
 #include <stdio.h>