[SPARK-23418][SQL] Fail DataSourceV2 reads when user schema is passed, but not supported.

## What changes were proposed in this pull request?

DataSourceV2 initially allowed user-supplied schemas when a source doesn't implement `ReadSupportWithSchema`, as long as the schema was identical to the source's schema. This is confusing behavior because changes to an underlying table can cause a previously working job to fail with an exception that user-supplied schemas are not allowed.

This reverts commit adcb25a0624, which was added to #20387 so that it could be removed in a separate JIRA issue and PR.

## How was this patch tested?

Existing tests.

Author: Ryan Blue <blue@apache.org>

Closes #20603 from rdblue/SPARK-23418-revert-adcb25a0624.