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tuple: remove useless loop from `tuple_dictionary_delete_hash`

Inside `tuple_dictionary_delete_hash`, there was a loop that, on each
iteration, searched for the first non-deleted element using `mh_first`,
which has a complexity of `O(n)`, and deleted it using `mh_strnu32_del`.
After the loop finished executing, `tuple_dictionary_delete_hash`
immediately called `mh_strnu32_delete`.
All elements are stored in the hashmap inplace, so `del` doesn't invoke
any memory deallocation functions. `del` also doesn't call destructors for
the elements; it merely sets a specific bit in the bitmap to 0.
Immediately after the loop, `mh_strnu32_delete(hash)` will delete the
hashmap `hash` along with the array `hash->p` containing all elements
inplace.

This commit simply removes this useless loop, which was causing
significant performance issues when closing a read view.

Closes tarantool/tarantool-ee#1043, #12115

NO_DOC=performance improvement
NO_TEST=performance improvement

(cherry picked from commit 4b720077b)

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