moulin: layers not removed from bblayers.conf when removed from manifest

[sa-kib]

Steps to reproduce:

• fill layers: section of manifest with sample layer names, e.g.:

[..]
layers:
        - "poky/meta"
        - "poky/meta-poky"
        - "poky/meta-yocto-bsp"
        - "meta-virtualization"
[..]

• generate bblayers.conf, e.g.:

$ ninja conf-dom0

• observe above layers in bblayers.conf, e.g.:

$ cat yocto/build/dom0/conf/bblayers.conf
[..] 
BBLAYERS ?= " \
  [..]/yocto/poky/meta \
  [..]/yocto/poky/meta-poky \
  [..]/yocto/poky/meta-yocto-bsp \
  [..]/yocto/meta-virtualization \
[..]

• remove some layer from layers: section of manifest, e.g.:

[..]
layers:
        - "poky/meta"
        - "poky/meta-poky"
        - "poky/meta-yocto-bsp"
 [..]

• re-generatate bblayers.conf:

$ touch yocto/build/dom0/conf/local.conf
$ ninja conf-dom0

• observe removed layer still present in Yocto configuration, e.g.:

$ cat yocto/build/dom0/conf/bblayers.conf
[..] 
BBLAYERS ?= " \
  [..]/yocto/poky/meta \
  [..]/yocto/poky/meta-poky \
  [..]/yocto/poky/meta-yocto-bsp \
  [..]/yocto/meta-virtualization \
[..]

• only after one manually removes file bblayers.conf & re-generates configuration it starts to reflect manifest changes

So since bitbake-layers add-layer only seems to be able to add layers, but not remove already added ones, we probably can remove bblayers,conf and start afresh each time configuration is updated.

[lorc]

Fixed via #94

[lorc]

The fix was reverted via #98, because it introduced an issue that seriously impaired day-to-day work.