strip UTF-8 BOM from PrintConfig.cpp, Print.cpp, Tab.cpp

The Linux CI build fails at the encoding-check step:
  "Source file is valid UTF-8 but contains a BOM mark"
These three files picked up a UTF-8 BOM (EF BB BF) during Windows-side
merges/edits. Removed the BOM (first 3 bytes only); file contents and line
endings are otherwise unchanged.

src/libslic3r/Print.cpp

@@ -1,4 +1,4 @@
-#include "Config.hpp"
+#include "Config.hpp"
 #include "Exception.hpp"
 #include "Print.hpp"
 #include "BoundingBox.hpp"

src/libslic3r/PrintConfig.cpp

@@ -1,4 +1,4 @@
-#include "PrintConfig.hpp"
+#include "PrintConfig.hpp"
 #include "PrintConfigConstants.hpp"
 #include "ClipperUtils.hpp"
 #include "Config.hpp"

src/slic3r/GUI/Tab.cpp

@@ -1,4 +1,4 @@
-// #include "libslic3r/GCodeSender.hpp"
+// #include "libslic3r/GCodeSender.hpp"
 //#include "slic3r/Utils/Serial.hpp"
 #include "Tab.hpp"
 #include "PresetHints.hpp"