chunk 1: remove unneeded bits to fix build with swig 4.1
from https://gitlab.com/kicad/code/kicad/-/issues/12414

Index: pcbnew/CMakeLists.txt
--- pcbnew/CMakeLists.txt.orig
+++ pcbnew/CMakeLists.txt
@@ -501,7 +501,7 @@ add_custom_command( OUTPUT ${CMAKE_CURRENT_BINARY_DIR}
     )
 
 if( UNIX AND NOT APPLE )
-    list( APPEND PCBNEW_EXTRA_LIBS rt )
+    list( APPEND PCBNEW_EXTRA_LIBS )
 endif()
 
 
