chore: remove all references to old include file

Remove all include statements for the old _replacevars.rst file. This is
no longer necessary and will result in substitution redefinition
warnings if users do not clean before building with the previous patch.

This was done using the following expression:

find source/ -name *.rst -exec sed -i '/.*include::.*_replacevars.*/,+1 d' {} \+

Signed-off-by: Randolph Sapp <[email protected]>

Author: StaticRocket