fix: remove a flaky set_error test

set_error was a flaky test due to a not thread-safe nature of mallinfo. We decided to remove it altogether after we check that tarantool::set_error! does not leak.

Demo

I made a simple demo with set_error macro calls that can be checked with valgrind: https://git.picodata.io/picodata/picodata/tarantool-module/-/tree/check-set-error

Setup

I ran the check in the following way:

cargo build -p set-error-test
valgrind --leak-check=yes tarantool set-error-test/run.lua

There I added two Rust function calls:

1. set_error executed 100 times
2. leak_mem which definitely leaks memory with std::mem::forget

Results

When both function calls were commented out, valgrind reports: definitely lost: 1,864 bytes in 4 blocks

When leak_mem only commented out: definitely lost: 1,864 bytes in 4 blocks

When set_error only commented out: definitely lost: 4,001,864 bytes in 5 blocks

Also for leak_mem valgrind showed a clear leak in Vec, nothing like that was shown for set_error.

I believe these proves that set_error! is leak free and we can remove this test.