smalltown -> metropolis

This pass removes all mentions of Smalltown, both from code and comments,
and replaces them with appropriate new terminology.

Test Plan: Refactor, covered by CI.

X-Origin-Diff: phab/D674
GitOrigin-RevId: 04a94d44ef07d46f7821530da5614daefe16d7ea
diff --git a/BUILD b/BUILD
index f855af7..df5db5b 100644
--- a/BUILD
+++ b/BUILD
@@ -94,13 +94,13 @@
     actual = "@com_github_go_delve_delve//cmd/dlv:dlv",
 )
 
-# Shortcut for launching a single Smalltown instance
+# Shortcut for launching a single Metropolis node instance in a VM.
 alias(
     name = "launch",
     actual = "//metropolis/test/launch/cli/launch",
 )
 
-# Shortcut for launching a virtual network with two Smalltown instances
+# Shortcut for launching a virtual network a Metropolis cluster consisting of two nodes.
 alias(
     name = "launch-multi2",
     actual = "//metropolis/test/launch/cli/launch-multi2",