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/toolchain/musl-host-gcc/sysroot/tarball.bzl b/build/toolchain/musl-host-gcc/sysroot/tarball.bzl
index 4f12049..5466690 100644
--- a/build/toolchain/musl-host-gcc/sysroot/tarball.bzl
+++ b/build/toolchain/musl-host-gcc/sysroot/tarball.bzl
@@ -22,7 +22,7 @@
 """
 Build a sysroot-style tarball containing musl/linux headers and libraries.
 
-This can then be used to build a C toolchain that builds for Smalltown.
+This can then be used to build a C toolchain that builds C/C++ binaries for Metropolis nodes.
 """
 
 def _musl_gcc_tarball(ctx):