LibC: Remove `#ifdef AK_OS_MACOS` checks from shadow.h

These checks were added because macOS doesn't have `shadow.h`, so we
would end up including our own LibC's `shadow.h` when we built Lagom.

All inclusions of this header in our code base are now guarded by
`#ifndef AK_OS_BSD_GENERIC`, so these checks are now pointless.

Userland/Libraries/LibC/shadow.h

@@ -6,9 +6,7 @@
 
 #pragma once
 
-#ifndef AK_OS_MACOS
-#    include <bits/FILE.h>
-#endif
+#include <bits/FILE.h>
 #include <sys/cdefs.h>
 #include <sys/types.h>
 
@@ -26,7 +24,6 @@ struct spwd {
     unsigned long int sp_flag;
 };
 
-#ifndef AK_OS_MACOS
 struct spwd* getspent(void);
 void setspent(void);
 void endspent(void);
@@ -38,6 +35,5 @@ int getspnam_r(const char* name, struct spwd* spbuf, char* buf, size_t buflen, s
 
 int fgetspent_r(FILE* fp, struct spwd* spbuf, char* buf, size_t buflen, struct spwd** spbufp);
 int sgetspent_r(const char* s, struct spwd* spbuf, char* buf, size_t buflen, struct spwd** spbufp);
-#endif
 
 __END_DECLS