BUILDFIX: copy/paste error in mesh autobuild.xml causes configure to fail.

copy/paste error in autobuild.xml caused INSTALL_PROPRIETARY to be set to TRUE
for OS builds. This causes configure to fail as llconvexdecomposition is not
available to OS devs. Changing INSTALL_PROPRIETARY to false for OS devs so
that llconvexdecompositionstub is used instead. problem only affects windows
builds.

autobuild.xml

@@ -2317,7 +2317,6 @@
                   <string>-G</string>
                   <string>"Visual Studio 10"</string>
                   <string>-DUNATTENDED:BOOL=ON</string>
-                  <string>-DINSTALL_PROPRIETARY=TRUE</string>
                   <string>-DUSE_KDU=FALSE</string>
                   <string>-DFMOD=FALSE</string>
                 </array>