py/mkenv.mk: Don't emit info about BUILD_VERBOSE if it's set.
py/mkenv.mk: Don't emit info about BUILD_VERBOSE if it's set.

If the user sets V or BUILD_VERBOSE then they don't need to see this
message.

Signed-off-by: Damien George <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@micropython.org>

adafruit/circuitpython,bvernoux/micropython,bvernoux/micropython,bvernoux/micropython,henriknelson/micropython,adafruit/circuitpython,adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,henriknelson/micropython,adafruit/circuitpython,adafruit/circuitpython,bvernoux/micropython,henriknelson/micropython,bvernoux/micropython,henriknelson/micropython