openjade/sgml-common: Add sstate postrm commands

openjade/sgml-common: Add sstate postrm commands

If you bump the PR of sgml-common and openjade-native but not sgml-
common-native, you will see a failure as files were removed from the
sysroot but still referenced by the sgml docbook catalog.

To properly handle this, the clean function needs to run at sstate
removal time, the problem is that this sstate removal can happen when
the metadata isn't present, so the correct removal commands are
unknown.

To avoid this, we need to write the commands into a "postrm" script
when we install the files, this can then be executed at sstate removal
time.

[YOCTO #8273]

(From OE-Core rev: cdae3e76232110903d124195b036e4e70fb28aa4)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>