Remove garbage collector macro from header (#114)

We can put this back the moment someone requests it. Pain-free garbage
collection for the C language is pretty cool. All it does is overwrite
the return address with a trampoline that calls free(). It's not clear
what it should be named if it's made a public API.

libc/mem/defer.greg.c

@@ -21,7 +21,7 @@
 #include "libc/calls/calls.h"
 #include "libc/mem/mem.h"
 #include "libc/nexgen32e/gc.internal.h"
-#include "libc/runtime/gc.h"
+#include "libc/runtime/gc.internal.h"
 #include "libc/runtime/runtime.h"
 
 forceinline bool PointerNotOwnedByParentStackFrame(struct StackFrame *frame,

libc/testlib/testlib.h

@@ -1,7 +1,7 @@
 #ifndef COSMOPOLITAN_LIBC_TESTLIB_H_
 #define COSMOPOLITAN_LIBC_TESTLIB_H_
 #include "libc/bits/weaken.h"
-#include "libc/runtime/gc.h"
+#include "libc/runtime/gc.internal.h"
 #include "libc/testlib/ugly.h"
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_