test: remove testcase with fractional datetime fields

There is no requirement for using fractional numbers
in datetime constructors. This issue will be addressed in [1].
The patch removes testcase with fractional numbers in datetime
constructor.

1. https://github.com/tarantool/tarantool/issues/10391

See also #10391
Needed for #10374

NO_CHANGELOG=testing
NO_DOC=testing

(cherry picked from commit 989c63c75f5f8c7b38dc67f8e5c32ce8bef1da08)