Revert " Define SIGSTOP 23 for architecture mips"

[safern]

Reverts #40299

This is causing System.Diagnostics.Process tests to crash in all Unix platforms with:

/private/tmp/helix/working/A5AE092E/w/A0C108D1/e /private/tmp/helix/working/A5AE092E/w/A0C108D1/e
  Discovering: System.Diagnostics.Process.Tests (method display = ClassAndMethod, method display options = None)
  Discovered:  System.Diagnostics.Process.Tests (found 221 of 291 test cases)
  Starting:    System.Diagnostics.Process.Tests (parallel test collections = on, max threads = 4)
    System.Diagnostics.Tests.ProcessStartInfoTests.ShellExecute_Nano_Fails_Start [SKIP]
      Condition(s) not met: "IsWindowsNanoServer"
Darwin
/Users/runner/work/1/s/src/libraries/Native/Unix/System.Native/pal_process.c (665): error 0: Unknown signal (false failed)
Assertion failed: (false && "assert_msg failed"), function SystemNative_Kill, file /Users/runner/work/1/s/src/libraries/Native/Unix/System.Native/pal_process.c, line 665.
./RunTests.sh: line 161: 42789 Abort trap: 6           "$RUNTIME_PATH/dotnet" exec --runtimeconfig System.Diagnostics.Process.Tests.runtimeconfig.json --depsfile System.Diagnostics.Process.Tests.deps.json xunit.console.dll System.Diagnostics.Process.Tests.dll -xml testResults.xml -nologo -nocolor -notrait category=IgnoreForCI -notrait category=OuterLoop -notrait category=failing $RSP_FILE

cc: @jkotas @Anipik

[Dotnet-GitSync-Bot]

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[jkotas]

Thanks!