Updated tools version to 2.0.0

Also merged lint-style (gofmt) into golangci-lint (enabled gofmt).
Also removed redundant lint-sanity (govet) which is already checked by golangci-lint.
Also made minor code changes to pass new golangci-lint tests.
Also changed lint-mod slightly so it reverts any changes it makes go.mod, go.sum, and vendor/.

VOL-2647

Change-Id: I15557edf0f9225ea1c44e5bab29481d17a82e2b8
diff --git a/db/model/branch.go b/db/model/branch.go
index 2066643..675c45d 100644
--- a/db/model/branch.go
+++ b/db/model/branch.go
@@ -166,7 +166,5 @@
 	b.mutex.Lock()
 	defer b.mutex.Unlock()
 
-	if _, ok := b.Revisions[hash]; ok {
-		delete(b.Revisions, hash)
-	}
+	delete(b.Revisions, hash)
 }