windows: Remove remaining traces of old GNU readline support.

GNU readline support for the unix port was removed in
acaa30b604 and in
5e83a75c78, so it's also no longer supported
in the windows port.

ports/windows/Makefile

@@ -46,9 +46,6 @@ OBJ = $(PY_O) $(addprefix $(BUILD)/, $(SRC_C:.c=.o))
 ifeq ($(MICROPY_USE_READLINE),1)
 CFLAGS_MOD += -DMICROPY_USE_READLINE=1
 SRC_C += lib/mp-readline/readline.c
-else ifeq ($(MICROPY_USE_READLINE),2)
-CFLAGS_MOD += -DMICROPY_USE_READLINE=2
-LDFLAGS_MOD += -lreadline
 endif
 
 LIB += -lws2_32

ports/windows/mpconfigport.h

@@ -26,7 +26,7 @@
 
 // options to control how MicroPython is built
 
-// Linking with GNU readline (MICROPY_USE_READLINE == 2) causes binary to be licensed under GPL
+// By default use MicroPython version of readline
 #ifndef MICROPY_USE_READLINE
 #define MICROPY_USE_READLINE        (1)
 #endif

ports/windows/mpconfigport.mk

@@ -3,7 +3,9 @@
 # Build 32-bit binaries on a 64-bit host
 MICROPY_FORCE_32BIT = 0
 
-# Linking with GNU readline causes binary to be licensed under GPL
+# This variable can take the following values:
+#  0 - no readline, just simple stdin input
+#  1 - use MicroPython version of readline
 MICROPY_USE_READLINE = 1
 
 # ffi module requires libffi (libffi-dev Debian package)