net/http/pprof: remove html/template dependency

net/http/pprof: remove html/template dependency

html/template indirectly uses reflect MethodByName, this causes linker
to use conservative mode resulting in larger binaries. The template here
is trivial and can be replaced by string manipulation.

This reduces a binary using only net/http/pprof by ~2.5MB.

Fixes #41569

Change-Id: I240e1daa6376182ff4961997ee3ec7b96cb07be8
Reviewed-on: https://go-review.googlesource.com/c/go/+/256900
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Hajime Hoshi <hajimehoshi@gmail.com>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Hajime Hoshi <hajimehoshi@gmail.com>
Trust: Brad Fitzpatrick <bradfitz@golang.org>