Remove LIBRARY_TYPE option from ctkMacroBuildPlugin

Plugins are expected to be shared library.

CMake/ctkMacroBuildPlugin.cmake

@@ -47,7 +47,7 @@
 #
 MACRO(ctkMacroBuildPlugin)
   CtkMacroParseArguments(MY
-    "EXPORT_DIRECTIVE;SRCS;MOC_SRCS;UI_FORMS;INCLUDE_DIRECTORIES;TARGET_LIBRARIES;RESOURCES;CACHED_RESOURCEFILES;TRANSLATIONS;LIBRARY_TYPE"
+    "EXPORT_DIRECTIVE;SRCS;MOC_SRCS;UI_FORMS;INCLUDE_DIRECTORIES;TARGET_LIBRARIES;RESOURCES;CACHED_RESOURCEFILES;TRANSLATIONS"
     "TEST_PLUGIN"
     ${ARGN}
     )
@@ -56,9 +56,9 @@ MACRO(ctkMacroBuildPlugin)
   IF(NOT DEFINED MY_EXPORT_DIRECTIVE)
     MESSAGE(SEND_ERROR "EXPORT_DIRECTIVE is mandatory")
   ENDIF()
-  IF(NOT DEFINED MY_LIBRARY_TYPE)
-    SET(MY_LIBRARY_TYPE "SHARED")
-  ENDIF()
+ 
+  # Plugin are expected to be shared library
+  SET(MY_LIBRARY_TYPE "SHARED")
 
   # Define library name
   SET(lib_name ${PROJECT_NAME})