Revert "Enable puma clustered (#654)" (#659)

This reverts commit 6c63546.

We don't know for sure that we need these speed/latency gains,
and maintenance bandwidth is low for the project.

We don't want to potentially have to track down bugs,
or undo any damage done, so revert this change for now.

config/puma.rb

@@ -21,7 +21,14 @@
 # Workers do not work on JRuby or Windows (both of which do not support
 # processes).
 #
-workers ENV.fetch("WEB_CONCURRENCY") { 3 }
+# workers ENV.fetch("WEB_CONCURRENCY") { 2 }
+
+# Use the `preload_app!` method when specifying a `workers` number.
+# This directive tells Puma to first boot the application and load code
+# before forking the application. This takes advantage of Copy On Write
+# process behavior so workers use less memory.
+#
+# preload_app!
 
 # Allow puma to be restarted by `rails restart` command.
 plugin :tmp_restart