build: upgrade to enchant-2
build: upgrade to enchant-2

- Remove enchant from RPM builds since docs are
  generated on ubuntu-20.04 in CI jobs.
- Clean up DEB_DEPENDS copy-pasta
- Add clang-11 for newest Ubuntu/Debian OS
  variants

Type: docs

Signed-off-by: Dave Wallace <0ed937c0e4b2f09f7bc24acf16cee52b8a199d5f@gmail.com>
Change-Id: I802f0b356bd412dbc23ee98d209f7cc3ab24ba4c

FDio/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,FDio/vpp,chrisy/vpp,chrisy/vpp