Date/Time: Remove incomplete and redundant test for `get_post_time()` added in [46580].

There is no functional difference between `gmt_offset` and `timezone_string` timezone modes for the issue.

See #48384.
Built from https://develop.svn.wordpress.org/trunk@46583


git-svn-id: https://core.svn.wordpress.org/trunk@46380 1a063a9b-81f0-0310-95a4-ce76da25c4cd