esp8266/etshal.h: Remove unneeded function declarations.
esp8266/etshal.h: Remove unneeded function declarations.

These removed ones are either unused by MicroPython or provided by osapi.h
in the SDK.  In particular ets_delay_us() has different signatures for
different versions of the SDK, so best to let it provide the declaration.

Fixes issue #8095.

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

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython