Remove unused internal member, shows that Config.DefaultHistogramBoundaries is unused (#2765)
Remove unused internal member, shows that Config.DefaultHistogramBoundaries is unused (#2765)

Signed-off-by: Bogdan Drutu <3f8e17047c2434e5c82a61403e56b9ef3e226d99@gmail.com>

Co-authored-by: Chester Cheung <760fe93daa1cebec1d1c06d4b99ae63131f99471@gmail.com>
open-telemetry/opentelemetry-go,open-telemetry/opentelemetry-go