MINOR: compression: Rename the function check_legacy_http_comp_flt()

To not mix it up with the legacy HTTP representation, this function has been
rename check_implicit_http_comp_flt().
diff --git a/include/proto/flt_http_comp.h b/include/proto/flt_http_comp.h
index 877cc9d..6e95f14 100644
--- a/include/proto/flt_http_comp.h
+++ b/include/proto/flt_http_comp.h
@@ -23,7 +23,6 @@
 
 #include <types/proxy.h>
 
-int check_legacy_http_comp_flt(struct proxy *proxy);
-
+int check_implicit_http_comp_flt(struct proxy *proxy);
 
 #endif // _PROTO_FLT_HTTP_COMP_H