Allow building without terminal library

This reverts commit 0d3416e0c2.
cf. https://github.com/tats/w3m/pull/221
Bug-Chromium: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=46629

acinclude.m4

@@ -427,9 +427,7 @@ AC_ARG_WITH(termlib,
  AC_MSG_RESULT($with_termlib)
  test x"$with_termlib" = xyes && with_termlib="terminfo mytinfo termlib termcap tinfo ncurses curses"
  for lib in $with_termlib; do
-   AC_CHECK_LIB($lib, tgetent,
-                [W3M_LIBS="$W3M_LIBS -l$lib"; break],
-                [test "$lib" = curses && AC_MSG_ERROR([No terminal library found])])
+   AC_CHECK_LIB($lib, tgetent, [W3M_LIBS="$W3M_LIBS -l$lib"; break])
  done
 ])
 #