[docs] Remove ref to deleted "Packaging.rst"

This is a fix for commit e9cdd16 ("[docs] Remove the Packaging
"Tips" which seems to be about pre-cmake ./configure (llvm#82958)"). The
doc was removed but not the references to it.

Author: bwendling

llvm/docs/GettingInvolved.rst

@@ -69,7 +69,6 @@ Information about LLVM's development process.
 
    Projects
    HowToReleaseLLVM
-   Packaging
    ReleaseProcess
    HowToAddABuilder
    ReleaseNotes
@@ -89,9 +88,6 @@ Information about LLVM's development process.
 :doc:`HowToAddABuilder`
    Instructions for adding new builder to LLVM buildbot master.
 
-:doc:`Packaging`
-   Advice on packaging LLVM into a distribution.
-
 :doc:`Release notes for the current release <ReleaseNotes>`
    This describes new features, known bugs, and other limitations.