[bsp][stm32] delete Kconfig $

bsp/stm32/stm32l053-st-nucleo/Kconfig

@@ -1,16 +1,16 @@
 mainmenu "RT-Thread Configuration"
 
-config $BSP_DIR
+config BSP_DIR
     string
     option env="BSP_ROOT"
     default "."
 
-config $RTT_DIR
+config RTT_DIR
     string
     option env="RTT_ROOT"
     default "../../.."
 
-config $PKGS_DIR
+config PKGS_DIR
     string
     option env="PKGS_ROOT"
     default "packages"