Revert "[AST] scan @_exported import modules of source files for display decls"

[shahmishal]

Reverts #40810

Release: https://ci.swift.org/view/Source%20Compatibility/job/swift-main-source-compat-suite/6379/
Debug: https://ci.swift.org/view/Source%20Compatibility/job/swift-main-source-compat-suite-debug/4420/

========================================
Failures:
  FAIL: fluent, 4.2, 270b6f, Swift Package
  FAIL: grpc-swift, 5.0, a45db1, Swift Package
  FAIL: async-http-client, 5.0, a72c5a, Swift Package
  FAIL: swift-nio-http2, 5.0, 492a77, Swift Package
  FAIL: swift-nio-extras, 5.0, 66f9a5, Swift Package
  FAIL: swift-nio-extras, 4.2, 0dbd54, Swift Package
  FAIL: swift-nio-ssl, 5.0, 6363cd, Swift Package
  FAIL: swift-nio-ssh, 5.0, 09778e, Swift Package
  FAIL: swift-nio-transport-services, 5.0, e7f527, Swift Package
  FAIL: swift-cluster-membership, 5.0, 0fd434, Swift Package
  FAIL: vapor_console, 4.2, 5b9796, Swift Package
  FAIL: vapor_core, 4.2, 08a576, Swift Package
  FAIL: vapor_database-kit, 4.2, 3a17db, Swift Package
  FAIL: vapor_multipart, 4.2, e57007, Swift Package
  FAIL: vapor_routing, 4.2, 3219e3, Swift Package
  FAIL: vapor_service, 4.2, 281a70, Swift Package
  FAIL: vapor_template-kit, 4.2, db35b1, Swift Package
  FAIL: vapor_url-encoded-form, 4.2, cbfe7e, Swift Package
  FAIL: vapor_validation, 4.2, 156f8a, Swift Package
  FAIL: mqtt-nio, 5.0, 17794a, Swift Package
========================================
Action Summary:
     Passed: 313
     Failed: 20
    XFailed: 20
    UPassed: 0
      Total: 353

[QuietMisdreavus]

This should also be applied to release/5.6, since the same patch was applied there, too.