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.expect

@@ -1,5 +0,0 @@
-abort = 111
-abort = 222
-abort = 333
-abort = 222
-abort = 111