text/template: remove an incorrect comment and clarify docs for AddParseTree
The comment "If the name is the name of this template, overwrite this template."
is incorrect and should be "is not" instead. This comment is no longer
required once the docs are updated to mention this behaviour instead.
Fixes #34695
Change-Id: I773495b2194d7bb7619b13c1a28cbc76e8f69aac
Reviewed-on: https://go-review.googlesource.com/c/go/+/199139 Reviewed-by: Rob Pike <r@golang.org>