ut: alloc-dealloc-mismatch (operator new [] vs free) in api_server_test

[vagetablechicken]

Ref #358

==7595==ERROR: AddressSanitizer: alloc-dealloc-mismatch (operator new [] vs free) on 0x60600024df40

https://github.com/4paradigm/OpenMLDB/blob/326295840f6c2932c2d47937f8cf0ddf6c238664/hybridse/include/base/fe_slice.h#L104 is new [], we should use delete [], not free.

[vagetablechicken]

But we don't just use new to create buf. We use malloc too. So we can't fix it until we fix all create methods. See all RefCountedSlice::CreateManaged argument buf.