remove python type backticks

This has been done to avoid a markdown to HTML rendering bug causing python code blocks to render the ampersand character as &amp; on the main host.  Example:
def set_dac(bitwise):
    set_pin(17, bitwise &amp; 1 == 1)
    set_pin(18, bitwise &amp; 2 == 2)
    set_pin(22, bitwise &amp; 4 == 4)
    set_pin(23, bitwise &amp; 8 == 8)