Not explicitly including "requirement modules"

[jerstlouis]

Including requirement modules multiple times currently causes warnings:

asciidoctor: WARNING: ../api_modules/bbox/requirements_module_bbox.adoc: line 3: id assigned to block already in use: rm_bbox
asciidoctor: WARNING: ../api_modules/bbox/requirements/REQ_rc-bbox-definition.adoc: line 3: id assigned to block already in use: req_collections_rc-bbox-definition
asciidoctor: WARNING: ../api_modules/bbox/requirements/REQ_rc-bbox-response.adoc: line 3: id assigned to block already in use: req_collections_rc-bbox-response
asciidoctor: WARNING: ../api_modules/datetime/requirements_module_datetime.adoc: line 3: id assigned to block already in use: rm_datetime
asciidoctor: WARNING: ../api_modules/datetime/requirements/REQ_rc-datetime-definition.adoc: line 3: id assigned to block already in use: req_collections_rc-datetime-definition
asciidoctor: WARNING: ../api_modules/datetime/requirements/REQ_rc-datetime-response.adoc: line 3: id assigned to block already in use: req_collections_rc-datetime-response

As previously discussed in this SWG as well as others (Maps/Tiles), suggesting that we do not explicitly include requirement modules, but instead instantiate their content directly in the sections of the document, allowing to tailor the content to adapt it to the context of the current requirement class.

[jerstlouis]

This has been applied and merged with #172.