Revert "[Support]Look up in top-level subcommand as a fallback when looking...

Revert "[Support]Look up in top-level subcommand as a fallback when looking options for a custom subcommand (#71975)

…ooking options for a custom subcommand. (#71776)"

This reverts commit b88308b1.

The build-bot is unhappy
(https://lab.llvm.org/buildbot/#/builders/186/builds/13096),
`GroupingAndPrefix` fails after `TopLevelOptInSubcommand` (the newly
added test).

Revert while I look into this (might be related with test sharding but
not sure)

```

[----------] 3 tests from CommandLineTest
[ RUN      ] CommandLineTest.TokenizeWindowsCommandLine2
[       OK ] CommandLineTest.TokenizeWindowsCommandLine2 (0 ms)
[ RUN      ] CommandLineTest.TopLevelOptInSubcommand
[       OK ] CommandLineTest.TopLevelOptInSubcommand (0 ms)
[ RUN      ] CommandLineTest.GroupingAndPrefix
 #0 0x00ba8118 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x594118)
 #1 0x00ba5914 llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x591914)
 #2 0x00ba89c4 SignalHandler(int) (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x5949c4)
 #3 0xf7828530 __default_sa_restorer /build/glibc-9MGTF6/glibc-2.31/signal/../sysdeps/unix/sysv/linux/arm/sigrestorer.S:67:0
 #4 0x00af91f0 (anonymous namespace)::CommandLineParser::ResetAllOptionOccurrences() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x4e51f0)
 #5 0x00af8e1c llvm::cl::ResetCommandLineParser() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x4e4e1c)
 #6 0x0077cda0 (anonymous namespace)::CommandLineTest_GroupingAndPrefix_Test::TestBody() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x168da0)
 #7 0x00bc5adc testing::Test::Run() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x5b1adc)
 #8 0x00bc6cc0 testing::TestInfo::Run() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x5b2cc0)
 #9 0x00bc7880 testing::TestSuite::Run() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x5b3880)
#10 0x00bd7974 testing::internal::UnitTestImpl::RunAllTests() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x5c3974)
#11 0x00bd6ebc testing::UnitTest::Run() (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x5c2ebc)
#12 0x00bb1058 main (/home/tcwg-buildbot/worker/clang-armv7-global-isel/stage1/unittests/Support/./SupportTests+0x59d058)
#13 0xf78185a4 __libc_start_main /build/glibc-9MGTF6/glibc-2.31/csu/libc-start.c:342:3
```