Removed warning box regarding SAMD21 builds
Removed warning box regarding SAMD21 builds

The support matrix shows that pulseio is supported for all SAMD21/SAMD51 variants. Removing warning to avoid confusion.
adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython