variables.rst: remove references to obsolete tar packaging

The tar packaging format was removed some time ago. Also, add some
minor grammatical tweaking.

(From yocto-docs rev: d62599595f68b75e5bf885367ca1f01a6d63bb3d)

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
(cherry picked from commit 8e9fd1ca232f3c1e8be51cb881a68b4745ee548a)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/ref-manual/variables.rst

@@ -4221,13 +4221,13 @@ system and gives an overview of their function and contents.
       variable.
 
    :term:`IMAGE_PKGTYPE`
-      Defines the package type (i.e. DEB, RPM, IPK, or TAR) used by the
+      Defines the package type (i.e. DEB, RPM or IPK) used by the
       OpenEmbedded build system. The variable is defined appropriately by
-      the :ref:`ref-classes-package_deb`, :ref:`ref-classes-package_rpm`,
-      or :ref:`ref-classes-package_ipk` class.
+      one of the :ref:`ref-classes-package_deb`, :ref:`ref-classes-package_rpm`,
+      or :ref:`ref-classes-package_ipk` classes.
 
       The :ref:`ref-classes-populate-sdk-*` and :ref:`ref-classes-image`
-      classes use the :term:`IMAGE_PKGTYPE` for packaging up images and SDKs.
+      classes use the :term:`IMAGE_PKGTYPE` for packaging images and SDKs.
 
       You should not set the :term:`IMAGE_PKGTYPE` manually. Rather, the
       variable is set indirectly through the appropriate
@@ -4236,12 +4236,6 @@ system and gives an overview of their function and contents.
       OpenEmbedded build system uses the first package type (e.g. DEB, RPM,
       or IPK) that appears with the variable
 
-      .. note::
-
-         Files using the ``.tar`` format are never used as a substitute
-         packaging format for DEB, RPM, and IPK formatted files for your image
-         or SDK.
-
    :term:`IMAGE_POSTPROCESS_COMMAND`
       Specifies a list of functions to call once the OpenEmbedded build
       system creates the final image output files. You can specify