Help: Drop FeatureSummary example in cmake-developer.7

The use of FeatureSummary inside a find module is not a convention
yet used by upstream CMake modules.  Drop the example from the
documentation about how to write find modules.  If in the future
we add use of FeatureSummary to many of the upstream find modules
then this example can be restored as part of establishing the
convention.
Help: Drop FeatureSummary example in cmake-developer.7

The use of FeatureSummary inside a find module is not a convention
yet used by upstream CMake modules.  Drop the example from the
documentation about how to write find modules.  If in the future
we add use of FeatureSummary to many of the upstream find modules
then this example can be restored as part of establishing the
convention.
Merge branch 'backport-doc-find-module-no-summary' into doc-find-module-no-summary

Resolve conflict in Help/manual/cmake-developer.7.rst by taking our
side.
Merge topic 'doc-find-module-no-summary' into next

3fb33e01 Merge branch 'backport-doc-find-module-no-summary' into doc-find-module-no-summary
d425c110 Help: Drop FeatureSummary example in cmake-developer.7
8235effe Help: Drop FeatureSummary example in cmake-developer.7