Clean up module import

- `import std.compat;` implies `import std;` so both aren't needed
- Add some initial build setup instructions to the MSVC regression test script

Author: hsutter

include/cpp2util.h

@@ -33,7 +33,6 @@
     //  If C++23 'import std;' was requested but isn't available, fall back
     //  to the 'include std' path
     #if defined(CPP2_IMPORT_STD) && defined(__cpp_lib_modules)
-        import std;
         import std.compat;
     //  If 'include std' was requested, include all standard headers.
     //  This list tracks the current draft standard, so as of this

regression-tests/test-results/msvc-2022/run-tests-msvc-2022.bat

@@ -1,6 +1,11 @@
 REM This is intended to be run in the /test-results/msvc-2022 directory
 REM in a VS2022 Command Prompt (which sets the path and other environment)
 REM
+REM After installing VS2022, to finish setting up std modules in your environment, run:
+REM     cl /std:c++latest /EHsc /nologo /W4 /MD /c "%VCToolsInstallDir%\modules\std.ixx"
+REM     cl /std:c++latest /EHsc /nologo /W4 /MD /c "%VCToolsInstallDir%\modules\std.compat.ixx"
+REM More info: https://learn.microsoft.com/en-us/cpp/cpp/tutorial-import-stl-named-module?view=msvc-170
+REM
 @echo off
 SETLOCAL EnableDelayedExpansion
 copy ..\*.cpp .