Remove unused host() method from AsyncWebServerRequest

Dead code with no callers. Also avoids an unchecked .value() on
optional<string> that would crash on HTTP/1.0 requests without
a Host header.

esphome/components/web_server_idf/web_server_idf.cpp

@@ -258,8 +258,6 @@ StringRef AsyncWebServerRequest::url_to(std::span<char, URL_BUF_SIZE> buffer) co
   return StringRef(buffer.data(), decoded_len);
 }
 
-std::string AsyncWebServerRequest::host() const { return this->get_header("Host").value(); }
-
 void AsyncWebServerRequest::send(AsyncWebServerResponse *response) {
   httpd_resp_send(*this, response->get_content_data(), response->get_content_size());
 }

esphome/components/web_server_idf/web_server_idf.h

@@ -121,7 +121,6 @@ class AsyncWebServerRequest {
     char buffer[URL_BUF_SIZE];
     return std::string(this->url_to(buffer));
   }
-  std::string host() const;
   // NOLINTNEXTLINE(readability-identifier-naming)
   size_t contentLength() const { return this->req_->content_len; }