undo "client_body_in_file_only any"
and introduce "client_body_in_file_only clean"

introduce ngx_pool_delete_file() to not break a possible third-party
ngx_pool_cleanup_file() usage that may lead to an removal of the useful files

delete unnecessary ngx_http_finalize_request_body()

src/http/ngx_http_request.h

diff --git a/src/http/ngx_http_request.h b/src/http/ngx_http_request.h
index 0c7f5cb..787b361 100644
--- a/src/http/ngx_http_request.h
+++ b/src/http/ngx_http_request.h
@@ -409,7 +409,7 @@
     unsigned                          request_body_in_single_buf:1;
     unsigned                          request_body_in_file_only:1;
     unsigned                          request_body_in_persistent_file:1;
-    unsigned                          request_body_delete_incomplete_file:1;
+    unsigned                          request_body_in_clean_file:1;
     unsigned                          request_body_file_group_access:1;
     unsigned                          request_body_file_log_level:3;