Update performance.md (#2016)

Remove duplicate cache-handler in the xcaddy build and replace the frankenphp module lines. The previous lines resulted in messages that php_server is not ordered. Perhaps these lines were outdated? This currently appears to work for me.

Author: silverbackdan

core/performance.md

@@ -41,8 +41,7 @@ The integration using the cache handler is quite simple. You just have to update
 +ENV CGO_ENABLED=1 XCADDY_SETCAP=1 XCADDY_GO_BUILD_FLAGS="-ldflags \"-w -s -extldflags '-Wl,-z,stack-size=0x80000'\""
 +RUN xcaddy build \
 +    --output /usr/local/bin/frankenphp \
-+    --with github.com/dunglas/frankenphp=./ \
-+    --with github.com/dunglas/frankenphp/caddy=./caddy/ \
++    --with github.com/dunglas/frankenphp/caddy \
 +    --with github.com/dunglas/mercure/caddy \
 +    --with github.com/dunglas/vulcain/caddy \
 +    --with github.com/dunglas/caddy-cbrotli \