[release-branch.go1.21] Revert "net/http: use Copy in ServeContent if CopyN not needed"
This reverts CL 446276.
Reason for revert: Causing surprising performance regression.
Fixes #61530
Change-Id: Ic970f2e05d875b606ce274ea621f7e4c8c337481
Reviewed-on: https://go-review.googlesource.com/c/go/+/512615
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit
df0a1297899aff1c46b66523e75aa12b0ff5049f)
Reviewed-on: https://go-review.googlesource.com/c/go/+/515795
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Damien Neil <dneil@google.com>