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/metropolis/node/core/tpm/tpm.go b/metropolis/node/core/tpm/tpm.go
index 76f4f92..4106a66 100644
--- a/metropolis/node/core/tpm/tpm.go
+++ b/metropolis/node/core/tpm/tpm.go
@@ -390,7 +390,7 @@
 	// store secrets on the OS side pre-global unlock and b) it makes no sense in this security model
 	// since an uncompromised host OS will not let an untrusted entity attest as itself and a
 	// compromised OS can either not pass PCR policy checks or the game's already over (you
-	// successfully runtime-exploited a production Smalltown Core)
+	// successfully runtime-exploited a production Metropolis node)
 	endorsementSession, _, err := tpm2.StartAuthSession(
 		tpm.device,
 		tpm2.HandleNull,