t5551: drop redundant grep for Accept-Language

t5551: drop redundant grep for Accept-Language

Commit b0c4adcdd7 (remote-curl: send Accept-Language header to server,
2022-07-11) added tests to make sure the header is sent via HTTP.
However, it checks in two places:

  1. In the expected trace output, we check verbatim for the header and
     its value.

  2. Afterwards, we grep for the header again in the trace file.

This (2) is probably cargo-culted from the earlier grep for
Accept-Encoding. It is needed for the encoding because we smudge the
value of that header when doing the verbatim check; see 1a53e692af
(remote-curl: accept all encodings supported by curl, 2018-05-22).

But we don't do so for the language header, so any problem that the
"grep" would catch in (2) would already have been caught by (1).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>