Stardardize underscore requirements in parameters across different ty…

…pe of

requests:
_index, _type, _source, _id keep their underscores
params like version and retry_on_conflict will be without underscores
Throw an error if older versions of parameters are used

BulkRequest, MultiGetRequest, TermVectorcRequest, MoreLikeThisQuery
were changed

Related to elastic#27040
Closes elastic#26886

docs/reference/migration/migrate_7_0/api.asciidoc

@@ -1,23 +1,24 @@
 [[breaking_70_api_changes]]
 === Breaking changes in 7.0
 
-==== Deprecated camel case and underscore parameters
+==== Camel case and underscore parameters deprecated in 6.x have been removed
+A  number of duplicate parameters deprecated in 6.x have been removed from
 Bulk request, Multi Get request, Term Vectors request, and More Like This Query
-requests have deprecated a number of duplicate parameters.
+requests.
 
-The following camel case parameters have been deprecated:
+The following camel case parameters have been removed:
 
 * `opType`
 * `versionType`, `_versionType`
 
-The following parameters starting with underscore have been deprecated:
+The following parameters starting with underscore have been removed:
 
 * `_parent`
 * `_retry_on_conflict`
 * `_routing`
 * `_version`
 * `_version_type`
 
-Instead of these deprecated parameters, use their non camel case equivalents without
+Instead of these removed parameters, use their non camel case equivalents without
 starting underscore, e.g. use `version_type` instead of `_version_type` or `versionType`.
 

rest-api-spec/src/main/resources/rest-api-spec/test/bulk/60_deprecated.yml

@@ -4,7 +4,7 @@
 
    - skip:
        version: " - 6.99.99"
-       reason:  some parameters are deprecated starting from 7.0, their equivalents without underscore are used instead
+       reason:  some parameters are removed starting from 7.0, their equivalents without underscore are used instead
        features: "warnings"
 
    - do:

rest-api-spec/src/main/resources/rest-api-spec/test/mget/80_deprecated.yml

@@ -4,7 +4,7 @@
 
    - skip:
        version: " - 6.99.99"
-       reason:  _version, _routing are deprecated starting from 7.0, their equivalents without underscore are used instead
+       reason:  _version, _routing are removed starting from 7.0, their equivalents without underscore are used instead
        features: "warnings"
 
    - do: