fix transformers script issues (#12802)
Fix a few obvious issues:
(1) bert_perf_test.py create session without provider in line 65.
(2) compare_bert_results.py miss a parameter in create_session in line 37
(3) onnx_exporter.py returns value mismatch in lines 667, 690.
(4) remove some imports not used in the scripts.
(5) fusion_utils need not print "Removed 0 cast nodes" or "Removed 0 Identity nodes"...
(6) update requirements for numpy version since gpt2 parity tool use equal_nan in numpy v1.19+
