NetServices: Remove Accept as standard and protected header.

In the old service kit, the Accept header was automatically set. However, it is
not a required header. This removes the default value and the protection against
setting it manually.

Required to make HaikuDepot work.

Change-Id: Ic589bfc5829db25915b67f2a13b6c2436c053e25

docs/user/netservices/HttpRequest.dox

@@ -652,7 +652,6 @@ namespace Network {
 
 	There are a few reserved fields, which cannot be set as optional fields. These currently are:
 	* \c Host
-	* \c Accept
 	* \c Accept-Encoding
 	* \c Connection
 	* \c Content-Type

src/kits/network/libnetservices2/HttpRequest.cpp

@@ -305,7 +305,6 @@ BHttpRequest::SetAuthentication(const BHttpAuthentication& authentication)
 
 static constexpr std::array<std::string_view, 6> fReservedOptionalFieldNames = {
 	"Host"sv,
-	"Accept"sv,
 	"Accept-Encoding"sv,
 	"Connection"sv,
 	"Content-Type"sv,
@@ -477,7 +476,6 @@ BHttpRequest::SerializeHeaderTo(BDataIO* target) const
 
 		outputFields.AddFields({
 			{"Host"sv, std::string_view(host.String())},
-			{"Accept"sv, "*"sv},
 			{"Accept-Encoding"sv, "gzip"sv},
 				// Allows the server to compress data using the "gzip" format.
 				// "deflate" is not supported, because there are two interpretations

src/tests/kits/net/netservices2/HttpProtocolTest.cpp

@@ -279,7 +279,6 @@ HttpProtocolTest::HttpMethodTest()
 constexpr std::string_view kExpectedRequestText =
 	"GET / HTTP/1.1\r\n"
 	"Host: www.haiku-os.org\r\n"
-	"Accept: *\r\n"
 	"Accept-Encoding: gzip\r\n"
 	"Connection: close\r\n"
 	"Api-Key: 01234567890abcdef\r\n\r\n";
@@ -343,7 +342,6 @@ private:
 constexpr std::string_view kExpectedStreamText =
 	"GET / HTTP/1.1\r\n"
 	"Host: www.haiku-os.org\r\n"
-	"Accept: *\r\n"
 	"Accept-Encoding: gzip\r\n"
 	"Connection: close\r\n\r\n";
 
@@ -542,7 +540,7 @@ static const BHttpFields kExpectedGetFields = {
 	{"Server"sv, "Test HTTP Server for Haiku"sv},
 	{"Date"sv, "Sun, 09 Feb 2020 19:32:42 GMT"sv},
 	{"Content-Type"sv, "text/plain"sv},
-	{"Content-Length"sv, "110"sv},
+	{"Content-Length"sv, "107"sv},
 	{"Content-Encoding"sv, "gzip"sv},
 };
 
@@ -553,7 +551,6 @@ constexpr std::string_view kExpectedGetBody = {
 	"Headers:\r\n"
 	"--------\r\n"
 	"Host: 127.0.0.1:PORT\r\n"
-	"Accept: *\r\n"
 	"Accept-Encoding: gzip\r\n"
 	"Connection: close\r\n"
 };
@@ -750,7 +747,6 @@ static BString kExpectedPostBody
 		"Headers:\r\n"
 		"--------\r\n"
 		"Host: 127.0.0.1:PORT\r\n"
-		"Accept: *\r\n"
 		"Accept-Encoding: gzip\r\n"
 		"Connection: close\r\n"
 		"Content-Type: text/plain\r\n"