Revert "* and #pragma pop_macro("macro_name")"

- pop_macro incorrect with initially undefined macro
- horrible implementation (tcc_open_bf)
- crashes eventually (abuse of Sym->prev_tok)

- the (unrelated) asm_label part is the opposite of a fix
  (Despite of its name this variable has nothing to do with
  the built-in assembler)

This reverts commit 0c8447db79.

tests/tests2/77_push_pop_macro.c

@@ -1,23 +0,0 @@
-#include <stdio.h>
-
-int main()
-{
-    #define abort "111"
-    printf("abort = %s\n", abort);
-
-    #pragma push_macro("abort")
-    #undef abort
-    #define abort "222"
-    printf("abort = %s\n", abort);
-
-    #pragma push_macro("abort")
-    #undef abort
-    #define abort "333"
-    printf("abort = %s\n", abort);
-
-    #pragma pop_macro("abort")
-    printf("abort = %s\n", abort);
-
-    #pragma pop_macro("abort")
-    printf("abort = %s\n", abort);
-}