kernel-dev: Removed another "don't" contraction.

(From yocto-docs rev: 1d839d54b914a54747afd965f93bb4a6d08d5fac)

Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/kernel-dev/kernel-dev-concepts-appx.xml

@@ -132,7 +132,7 @@
                 The "Yocto Project Baseline Kernel" contains functionality that is common to every kernel
                 type and BSP that is organized further up the tree.
                 Placing these common features in the
-                tree this way means features don't have to be duplicated along individual branches of the
+                tree this way means features do not have to be duplicated along individual branches of the
                 structure.
             </para>
             <para>