docs: Remove old docs that mention setting up a build environment with lib.exe

The build system doesn't use lib.exe any longer, and therefore this
can be simplified.
Signed-off-by: Martin Storsjö <martin@martin.st>

doc/general.texi

@@ -923,30 +923,7 @@ Libav, so you must add this line before @code{#include}ing libav*:
 
 This is how to create DLL and LIB files that are compatible with MSVC++:
 
-@enumerate
-
-@item Add a call to @file{vcvars32.bat} (which sets up the environment
-variables for the Visual C++ tools) as the first line of @file{msys.bat}.
-The standard location for @file{vcvars32.bat} is
-@file{C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat},
-and the standard location for @file{msys.bat} is @file{C:\msys\1.0\msys.bat}.
-If this corresponds to your setup, add the following line as the first line
-of @file{msys.bat}:
-
-@example
-call "C:\Program Files\Microsoft Visual Studio 8\VC\bin\vcvars32.bat"
-@end example
-
-Alternatively, you may start the @file{Visual Studio 2005 Command Prompt},
-and run @file{c:\msys\1.0\msys.bat} from there.
-
-@item Within the MSYS shell, run @code{lib.exe}. If you get a help message
-from @file{Microsoft (R) Library Manager}, this means your environment
-variables are set up correctly, the @file{Microsoft (R) Library Manager}
-is on the path and will be used by Libav to create
-MSVC++-compatible import libraries.
-
-@item Build Libav with
+Within the MSYS shell, build Libav with
 
 @example
 ./configure --enable-shared
@@ -957,8 +934,6 @@ make install
 Your install path (@file{/usr/local/} by default) should now have the
 necessary DLL and LIB files under the @file{bin} directory.
 
-@end enumerate
-
 To use those files with MSVC++, do the same as you would do with
 the static libraries, as described above. But in Step 4,
 you should only need to add the directory where the LIB files are installed