Rename all test files: remove _test suffix

Prepare test files for Ginkgo migration by renaming:

test/e2e/:
- bound_sa_token_test.go → bound_sa_token.go
- certrotation_test.go → certrotation.go
- deprecated_api_test.go → deprecated_api.go
- encryption_test.go → encryption.go
- operator_test.go → operator.go
- serviceaccountissuer_test.go → serviceaccountissuer.go
- user_certs_test.go → user_certs.go
- user_client_ca_test.go → user_client_ca.go
- user_cors_test.go → user_cors.go

test/e2e-encryption/:
- encryption_test.go → encryption.go
- main_test.go (removed - no longer needed)

test/e2e-encryption-perf/:
- encryption_perf_test.go → encryption_perf.go

test/e2e-encryption-rotation/:
- encryption_rotation_test.go → encryption_rotation.go

test/e2e-sno-disruptive/:
- sno_disruptive_test.go → sno_disruptive.go

No content changes in this commit - pure renames only.

Author: gangwgr