Don't show branch heads in reflog subcommits

It's tricky to get this right for reflog commits wrt what's the current branch
for each one; so just disable it entirely here, it's probably not something
anybody needs here.

pkg/gui/context/reflog_commits_context.go

@@ -86,3 +86,7 @@ func (self *ReflogCommitsContext) GetDiffTerminals() []string {
 
 	return []string{itemId}
 }
+
+func (self *ReflogCommitsContext) ShowBranchHeadsInSubCommits() bool {
+	return false
+}