std: delete psapi, gdi32, and winmm

The only remaining Windows APIs now are the ones that the standard
library itself depends on for its cross-platform abstractions.

closes #4426

Author: andrewrk

lib/std/os/windows.zig

@@ -22,11 +22,8 @@ pub const advapi32 = @import("windows/advapi32.zig");
 pub const kernel32 = @import("windows/kernel32.zig");
 pub const ntdll = @import("windows/ntdll.zig");
 pub const ole32 = @import("windows/ole32.zig");
-pub const psapi = @import("windows/psapi.zig");
 pub const shell32 = @import("windows/shell32.zig");
 pub const ws2_32 = @import("windows/ws2_32.zig");
-pub const gdi32 = @import("windows/gdi32.zig");
-pub const winmm = @import("windows/winmm.zig");
 pub const crypt32 = @import("windows/crypt32.zig");
 pub const nls = @import("windows/nls.zig");