librem5_defconfig: make USB gadget configuration similar to Debian

remove many of the legacy precomposed USB gadget configurations and
enable all of the configfs/functionfs capabilities.
2 jobs for remove_g_multi in 65 minutes and 52 seconds
Status Job ID Name Coverage
  Build
passed #363928
librem5
build:aarch64

00:36:19

passed #363929
librem5:arm64
build:deb

01:05:52