Remove obsolete documentation related to pushing to refs/changes/

Change I99f6d400b removed support for push to refs/changes/ but left
various documentation that still refers to it.

Change-Id: I2f026033885ba145230c9bda511d27cba6094a77

Documentation/error-change-does-not-belong-to-project.txt

@@ -1,18 +0,0 @@
-= change ... does not belong to project ...
-
-With this error message Gerrit rejects to push a commit to a change
-that belongs to another project.
-
-This error message means that the user explicitly pushed a commit to
-a change that belongs to another project by specifying it as target
-ref. This way of adding a new patch set to a change is deprecated as
-explained link:user-upload.html#manual_replacement_mapping[here]. It is recommended to only rely on Change-Ids for
-link:user-upload.html#push_replace[replacing changes].
-
-
-GERRIT
-------
-Part of link:error-messages.html[Gerrit Error Messages]
-
-SEARCHBOX
----------

Documentation/error-change-not-found.txt

@@ -1,17 +0,0 @@
-= change ... not found
-
-With this error message Gerrit rejects to push a commit to a change
-that cannot be found.
-
-This error message means that the user explicitly pushed a commit to
-a non-existing change by specifying it as target ref. This way of
-adding a new patch set to a change is deprecated as explained link:user-upload.html#manual_replacement_mapping[here].
-It is recommended to only rely on Change-Ids for link:user-upload.html#push_replace[replacing changes].
-
-
-GERRIT
-------
-Part of link:error-messages.html[Gerrit Error Messages]
-
-SEARCHBOX
----------

Documentation/error-messages.txt

@@ -9,8 +9,6 @@ occurring and what can be done to solve it.
 
 * link:error-branch-not-found.html[branch ... not found]
 * link:error-change-closed.html[change ... closed]
-* link:error-change-does-not-belong-to-project.html[change ... does not belong to project ...]
-* link:error-change-not-found.html[change ... not found]
 * link:error-commit-already-exists.html[commit already exists]
 * link:error-contains-banned-commit.html[contains banned commit ...]
 * link:error-has-duplicates.html[... has duplicates]
@@ -35,7 +33,6 @@ occurring and what can be done to solve it.
 * link:error-same-change-id-in-multiple-changes.html[same Change-Id in multiple changes]
 * link:error-too-many-commits.html[too many commits]
 * link:error-upload-denied.html[Upload denied for project \'...']
-* link:error-push-refschanges-not-allowed.html[upload to refs/changes not allowed]
 * link:error-not-allowed-to-upload-merges.html[you are not allowed to upload merges]
 
 

Documentation/error-push-refschanges-not-allowed.txt

@@ -1,13 +0,0 @@
-= upload to refs/changes not allowed
-
-Pushing to `refs/changes/` is deprecated and is not allowed on this Gerrit server.
-See the documentation for link:user-upload.html#push_create[creating changes] for
-alternate ways to push to existing changes.
-
-
-GERRIT
-------
-Part of link:error-messages.html[Gerrit Error Messages]
-
-SEARCHBOX
----------

Documentation/user-upload.txt

@@ -465,9 +465,6 @@ If Change-Id lines are not present in the commit messages, consider
 amending the message and copying the line from the change's page
 on the web, and then using `git push` as described above.
 
-If Change-Id lines are not available, then the user must use the
-manual mapping technique described below.
-
 For more about Change-Ids, see link:user-changeid.html[Change-Id Lines].
 
 
@@ -653,10 +650,6 @@ If Change-Id lines are not present in the commit messages, consider
 amending the message and copying the line from the change's page
 on the web.
 
-If Change-Id lines are not available, then the user must use the much
-more <<manual_replacement_mapping,manual mapping technique>> offered
-by using `git push` to a specific `refs/changes/change#` reference.
-
 For more about Change-Ids, see link:user-changeid.html[Change-Id Lines].