Rename machines to main to avoid dispatch. (#2551)

Author: chriseth

test_data/asm/book/assert_write_register.asm

@@ -1,4 +1,4 @@
-machine Machine with degree: 8 {
+machine Main with degree: 8 {
     // ANCHOR: component
 reg pc[@pc];
 reg A;

test_data/asm/single_function_vm.asm

@@ -1,7 +1,10 @@
-machine VM with degree: 8 {
+machine Main with degree: 8 {
     reg pc[@pc];
+    reg X[<=];
+    reg A;
 
     function main {
+        A <=X= A + 1;
         return;
     }
 }