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>