pw_docgen: Disable banner due to unicode (Windows)
pw_docgen: Disable banner due to unicode (Windows)

This disables printing the banner in docgen, since it is currently
breaking the Windows doc build. Eventually this should get re-enabled
once the root issue is addressed.

Bug: pwbug/164
Change-Id: I9cf17edd2f5f83b3da99fc2319fa23fdeea3a45b

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed