Clean up terms "delete timeline" and "detach tenant".

You cannot attach/detach an individual timeline, attach/detach always
applies to the whole tenant. However, you can *delete* a single timeline
from a tenant. Fix some comments and error messages that confused these
two operations.

pageserver/src/tenant.rs

@@ -346,7 +346,7 @@ impl Tenant {
 
         ensure!(
             !children_exist,
-            "Cannot detach timeline which has child timelines"
+            "Cannot delete timeline which has child timelines"
         );
         let timeline_entry = match timelines.entry(timeline_id) {
             Entry::Occupied(e) => e,

test_runner/regress/test_normal_work.py

@@ -39,7 +39,7 @@ def test_normal_work(neon_env_builder: NeonEnvBuilder, num_timelines: int, num_s
     * restart compute
     * check that the data is there
     * stop compute
-    * detach timeline
+    * detach tenant
 
     Repeat check for several tenants/timelines.
     """

test_runner/regress/test_tenant_detach.py

@@ -70,7 +70,7 @@ def test_tenant_detach_smoke(neon_env_builder: NeonEnvBuilder):
             break
     # else is called if the loop finished without reaching "break"
     else:
-        pytest.fail(f"could not detach timeline: {last_error}")
+        pytest.fail(f"could not detach tenant: {last_error}")
 
     gc_thread.join(timeout=10)
 

test_runner/regress/test_timeline_delete.py

@@ -32,7 +32,7 @@ def test_timeline_delete(neon_simple_env: NeonEnv):
 
     ps_http = env.pageserver.http_client()
     with pytest.raises(
-        NeonPageserverApiException, match="Cannot detach timeline which has child timelines"
+        NeonPageserverApiException, match="Cannot delete timeline which has child timelines"
     ):
 
         timeline_path = (