Remove polylith/API mode (#2967)

This removes most of the code used for polylith/API mode.

This removes the `/api` internal endpoints entirely. 

Binary size change roughly 5%: 
```
51437560 Feb 13 10:15 dendrite-monolith-server # old
48759008 Feb 13 10:15 dendrite-monolith-server # new
```

build/scripts/complement-cmd.sh

@@ -4,19 +4,17 @@
 
 if [[ "${COVER}" -eq 1 ]]; then
   echo "Running with coverage"
-  exec /dendrite/dendrite-monolith-server-cover \
+  exec /dendrite/dendrite-cover \
     --really-enable-open-registration \
     --tls-cert server.crt \
     --tls-key server.key \
     --config dendrite.yaml \
-    -api=${API:-0} \
     --test.coverprofile=complementcover.log
 else
   echo "Not running with coverage"
-  exec /dendrite/dendrite-monolith-server \
+  exec /dendrite/dendrite \
     --really-enable-open-registration \
     --tls-cert server.crt \
     --tls-key server.key \
-    --config dendrite.yaml \
-    -api=${API:-0}
+    --config dendrite.yaml
 fi