Remove references to high availability

Per discussion from GitLab executives, remove mentions of high
availability.

doc/administration/file_hooks.md

@@ -35,8 +35,8 @@ Follow the steps below to set up a custom hook:
    `/home/git/gitlab/file_hooks/`. For Omnibus installs the path is
    usually `/opt/gitlab/embedded/service/gitlab-rails/file_hooks`.
 
-    For [highly available](reference_architectures/index.md) configurations, your hook file should exist on each
-    application server.
+    For [configurations with multiple servers](reference_architectures/index.md),
+    your hook file should exist on each application server.
 
 1. Inside the `file_hooks` directory, create a file with a name of your choice,
    without spaces or special characters.

doc/administration/geo/replication/datatypes.md

@@ -79,7 +79,7 @@ GitLab stores files and blobs such as Issue attachments or LFS objects into eith
   - A Storage Appliance that exposes an Object Storage-compatible API.
 
 When using the filesystem store instead of Object Storage, you need to use network mounted filesystems
-to run GitLab when using more than one server (for example with a High Availability setup).
+to run GitLab when using more than one server.
 
 With respect to replication and verification:
 

doc/administration/geo/replication/external_database.md

@@ -153,8 +153,7 @@ To configure the connection to the external read-replica database and enable Log
 **Secondary** nodes use a separate PostgreSQL installation as a tracking
 database to keep track of replication status and automatically recover from
 potential replication issues. Omnibus automatically configures a tracking database
-when `roles ['geo_secondary_role']` is set. For high availability,
-refer to [Geo High Availability](../../reference_architectures/index.md).
+when `roles ['geo_secondary_role']` is set.
 If you want to run this database external to Omnibus, please follow the instructions below.
 
 The tracking database requires an [FDW](https://www.postgresql.org/docs/11/postgres-fdw.html)