Revert "Proposal to add barrier configs for showDatePicker, showTimePicker and showAboutDialog."

[loic-sharma]

Reverts #130484. /cc @ronnnnn

Example failure: https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/12185/overview

Failure logs...

04:51 +5379 ~18: /Volumes/Work/s/w/ir/x/w/flutter/packages/flutter/test/material/about_test.dart: Barrier dismissible Barrier is dismissible with default parameter                                    
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure was thrown running a test:
Expected: <1>
  Actual: <2>

When the exception was thrown, this was the stack:
#4      main.<anonymous closure>.<anonymous closure> (file:///Volumes/Work/s/w/ir/x/w/flutter/packages/flutter/test/material/about_test.dart:776:7)
<asynchronous suspension>
#5      testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:165:15)
<asynchronous suspension>
#6      TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:1008:5)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

This was caught by the test expectation on the following line:
  file:///Volumes/Work/s/w/ir/x/w/flutter/packages/flutter/test/material/about_test.dart line 776
The test description was:
  Barrier is dismissible with default parameter
════════════════════════════════════════════════════════════════════════════════════════════════════

04:51 +5379 ~18 -1: /Volumes/Work/s/w/ir/x/w/flutter/packages/flutter/test/material/about_test.dart: Barrier dismissible Barrier is dismissible with default parameter [E]                             
  Test failed. See exception logs above.
  The test description was: Barrier is dismissible with default parameter
  

To run this test again: /Volumes/Work/s/w/ir/x/w/flutter/bin/cache/dart-sdk/bin/dart test /Volumes/Work/s/w/ir/x/w/flutter/packages/flutter/test/material/about_test.dart -p vm --plain-name 'Barrier dismissible Barrier is dismissible with default parameter'