tests/extmod/framebuf_polygon.py: Replace sys.stdout.write with print.

So the test doesn't depend on the `sys` module.

Signed-off-by: Damien George <damien@micropython.org>

tests/extmod/framebuf_polygon.py

@@ -1,5 +1,3 @@
-import sys
-
 try:
     import framebuf
     from array import array
@@ -18,8 +16,8 @@ def print_buffer(buffer, width, height):
     for row in range(height):
         for col in range(width):
             val = buffer[(row * width) + col]
-            sys.stdout.write(" {:02x}".format(val) if val else " ··")
-        sys.stdout.write("\n")
+            print(" {:02x}".format(val) if val else " ··", end="")
+        print()
 
 
 buf = bytearray(70 * 70)