FindBoost: Add policy to remove this module
Upstream Boost 1.70 and above provide a proper BoostConfig.cmake
package configuration file. Packages for all major distros now
provide it in at least one LTS release. Add a policy to pretend
that the FindBoost
module does not exist so that projects calling
find_package(Boost)
use the upstream package directly.
Closes: #19402 (closed)