HeadscaleAPI: replace Echo server with Gorilla Mux

Change-Id: Ie1109cb0a981844c91dd0948592dccf0090c1961
diff --git a/core/headscale/go.mod b/core/headscale/go.mod
index 783dc19..c2c1616 100644
--- a/core/headscale/go.mod
+++ b/core/headscale/go.mod
@@ -2,16 +2,4 @@
 
 go 1.18
 
-require github.com/labstack/echo/v4 v4.10.2
-
-require (
-	github.com/labstack/gommon v0.4.0 // indirect
-	github.com/mattn/go-colorable v0.1.13 // indirect
-	github.com/mattn/go-isatty v0.0.17 // indirect
-	github.com/valyala/bytebufferpool v1.0.0 // indirect
-	github.com/valyala/fasttemplate v1.2.2 // indirect
-	golang.org/x/crypto v0.6.0 // indirect
-	golang.org/x/net v0.7.0 // indirect
-	golang.org/x/sys v0.5.0 // indirect
-	golang.org/x/text v0.7.0 // indirect
-)
+require github.com/gorilla/mux v1.8.1