db: fix db3/db4 confusion by causing all packages to use virtual/db in db-4.3 4.3.29

db: fix db3/db4 confusion by causing all packages to use virtual/db in db-4.3 4.3.29
  - The SleepyCat implementation of the Berkeley DB exists in OE in two different
  - versions, 3.2 and 4.3.  These appear to now be compatible (i.e. with the correct
  - settings db-4.3 can do everything db-3.2 can do and all packages compile with it).
  - The previous scheme of allowing both to be built (which was highly error prone)
  - has been removed and all db users now reference virtual/db.
  - Affects:
  - bogofilter, cyrus-*, openldap, perl, postfix, rpm