webos: Remove duplicite INHERIT settings

* All classes were inherited twice:
  $INHERIT [6 operations]
    append conf/local.conf:24
      "buildhistory"
    append conf/local.conf:37
      "rm_work"
    append conf/local.conf:57
      "webos-ports-mirrors"
    append meta-webos/conf/distro/webos.conf:60
      "${PACKAGE_CLASSES} ${USER_CLASSES} ${INHERIT_INSANE} ${INHERIT_DISTRO}"
    append openembedded-core/meta/conf/distro/defaultsetup.conf:22
      "${PACKAGE_CLASSES} ${USER_CLASSES} ${INHERIT_INSANE} ${INHERIT_DISTRO}"
    append openembedded-core/meta/conf/sanity.conf:15
      "sanity"
  computed:
    " buildhistory rm_work webos-ports-mirrors ${PACKAGE_CLASSES} ${USER_CLASSES} ${INHERIT_INSANE} ${INHERIT_DISTRO} ${PACKAGE_CLASSES} ${USER_CLASSES} ${INHERIT_INSANE} ${INHERIT_DISTRO} sanity"
  INHERIT="buildhistory rm_work webos-ports-mirrors package_ipk  insane debian devshell sstate license webos_base package_ipk  insane debian devshell sstate license webos_base sanity"

* PACKAGE_CLASSES and INHERIT_INSANE were set to the same default value
  as in defaultsetup.conf

[GF-2417] Reorganize distro configs

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@palm.com>
Change-Id: Ie6ebcc8530ca7149ff9761f6a5000797fb99895c
Reviewed-on: https://g2g.palm.com/1712
Reviewed-by: Martin Jansa <martin.jansa@palm.com>
Tested-by: Martin Jansa <martin.jansa@palm.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>