Rename cmd/main.go to cmd/canoninja.go

So that it can be built and installed with
````
(cd build/make/tools/canoninja && go install cmd/canoninja.go)
```

Bug: 201713929
Test: internal
Change-Id: I38133bf26ccfae5ebf8bc3c68bc595b7274576b9
diff --git a/tools/canoninja/cmd/main.go b/tools/canoninja/cmd/canoninja.go
similarity index 100%
rename from tools/canoninja/cmd/main.go
rename to tools/canoninja/cmd/canoninja.go