esp32/usb: Further improve speed of USB CDC output.
esp32/usb: Further improve speed of USB CDC output.

Following on from ba940250a5b630018c8d9b0e21c5ed858a20450f, the change here
makes output about 15 times faster (now up to about 550 kbytes/sec).

tinyusb_cdcacm_write_queue will return the number of bytes written, so
there's no need to use tud_cdc_n_write_available.

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

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