html/template: remove unused `mode` field on `Tree` struct

This changes Go, to remove this unused field on the `Tree` struct. Which seems to replaced by the non-private field `Mode`.

Change-Id: I5b384424cf60aa0af36eb8aad1d8db3f99b9838e
GitHub-Last-Rev: 4b033f967b55ff99df8a969ac1c91c358b82b726
GitHub-Pull-Request: golang/go#48028
Reviewed-on: https://go-review.googlesource.com/c/go/+/345789
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
diff --git a/src/text/template/parse/parse.go b/src/text/template/parse/parse.go
index d92bed5..64b29a2 100644
--- a/src/text/template/parse/parse.go
+++ b/src/text/template/parse/parse.go
@@ -32,7 +32,6 @@
 	treeSet    map[string]*Tree
 	actionLine int // line of left delim starting action
 	rangeDepth int
-	mode       Mode
 }
 
 // A mode value is a set of flags (or 0). Modes control parser behavior.