cmake: restore old behavior for savedefconfig

savedefconfig shouldn't overwrite the original defconfig, but only create a new
defconfig in the current directory. Otherwise, creating new configs based on
existing ones becomes irritating, because every time we use savedefconfig,
the original configuration is overwritten which is not the excepted behavior

cmake/menuconfig.cmake

@@ -98,8 +98,6 @@ add_custom_target(
   COMMAND echo "\\#" >> ${CMAKE_BINARY_DIR}/warning.tmp
   COMMAND cat ${CMAKE_BINARY_DIR}/warning.tmp
           ${CMAKE_BINARY_DIR}/sortedconfig.tmp > ${CMAKE_BINARY_DIR}/defconfig
-  COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_BINARY_DIR}/defconfig
-          ${NUTTX_DEFCONFIG}
   COMMAND ${CMAKE_COMMAND} -E remove -f ${CMAKE_BINARY_DIR}/warning.tmp
   COMMAND ${CMAKE_COMMAND} -E remove -f ${CMAKE_BINARY_DIR}/defconfig.tmp
   COMMAND ${CMAKE_COMMAND} -E remove -f ${CMAKE_BINARY_DIR}/sortedconfig.tmp