[HOTFIX][SQL] Fix the failed test cases in GeneratorFunctionSuite

### What changes were proposed in this pull request?
Multiple tests failed. Revert the changes on `supportCodegen` of `GenerateExec`. For example,

- https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder/75194/testReport/

### How was this patch tested?
N/A

Author: Xiao Li <gatorsmile@gmail.com>

Closes #17425 from gatorsmile/turnOnCodeGenGenerateExec.