[Snek] [keith-packard/snek] 46d40b: ports/mega: Remove USBSERIAL_HEX from mega install

[Keith Packard]

  Branch: refs/heads/main
  Home:   https://github.com/keith-packard/snek
  Commit: 46d40bff932e775b580f312364f157615fcd5811
      https://github.com/keith-packard/snek/commit/46d40bff932e775b580f312364f157615fcd5811
  Author: Keith Packard <keithp at keithp.com>
  Date:   2021-02-05 (Fri, 05 Feb 2021)

  Changed paths:
    M ports/mega/Makefile

  Log Message:
  -----------
  ports/mega: Remove USBSERIAL_HEX from mega install

This file isn't present anymore

Signed-off-by: Keith Packard <keithp at keithp.com>