CLEANUP: mux-quic: remove unused attribute on qcs_is_close_remote()

qcs_is_close_remote() is used in qcc_decode_qcs(). Thus the unused
function attribute is now unneeded.

This can be backported up to 2.7.
diff --git a/src/mux_quic.c b/src/mux_quic.c
index 89da1e6..9d7bcf5 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -373,7 +373,7 @@
 	return qcs->st == QC_SS_HLOC || qcs->st == QC_SS_CLO;
 }
 
-static __maybe_unused int qcs_is_close_remote(struct qcs *qcs)
+static int qcs_is_close_remote(struct qcs *qcs)
 {
 	return qcs->st == QC_SS_HREM || qcs->st == QC_SS_CLO;
 }