CDRIVER-5565 remove non-API docs (#1600)

* libmongoc: remove links to content moved to mongodb.com

The API and APM docs are linked to from mongodb.com.

* libmongoc: remove no-longer-referenced files

* libmongoc: remove `genindex`

The index page only shows one entry for `mongoc_kms_credentials_provider_callback_fn`.

* libmongoc: link to `MongoDB C Driver` page

* libmongoc: fix links to `queryable-encryption`

* libmongoc: fix links to `authentication`

* libmongoc: fix links to `bulk`

* libmongoc: fix links to `client-side-field-level-encryption`

* libmongoc: fix links to `configuring_tls`

* libmongoc: fix links to `connection-pooling`

* libmongoc: fix links to `in-use-encryption`

* libmongoc: fix links to `manage-collection-indexes`

* libmongoc: fix links to ``setting_collation_order`

* libmongoc: fix links to `tutorial_crud_operations`

* libmongoc: fix link to `bulk_operation_bypassing_document_validation`

* libmongoc: fix links to `cursors_tailable`

* libbson: remove links to content moved to mongodb.com

The API docs are linked to from mongodb.com.

* libbson: link to `MongoDB C Driver` page

* libbson: remove no-longer-referenced files

* libbson: fix links to `errors`

* libmongoc: fix links to `bson:errors`

* libmongoc: fix links to `bson:lifetimes`

* homepage: link to `MongoDB C Driver` page

* libmongoc: remove no-longer-used images

* libmongoc: remove unreferenced include

* update links in README

* update link in CONTRIBUTING.md

* fix links to community forums

* add missing "the"

Co-authored-by: Roberto C. Sánchez <roberto@connexer.com>

* fix `setting_collation_order_` links

Co-authored-by: Roberto C. Sánchez <roberto@connexer.com>

* fix `setting_collation_order_` in `generate-opts.py`

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Co-authored-by: Roberto C. Sánchez <roberto@connexer.com>