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.

tcctok.h

@@ -155,8 +155,6 @@
 #endif
      DEF(TOK_comment, "comment")
      DEF(TOK_lib, "lib")
-     DEF(TOK_push_macro, "push_macro")
-     DEF(TOK_pop_macro, "pop_macro")
      DEF(TOK_once, "once")
 
 /* builtin functions or variables */