Merge #19257: build: remove BIP70 configure option

c4ffcf0 build: remove BIP70 configure option (fanquake)

Pull request description:

  This was left in after #17165, so that anyone who had been compiling
  with (already disabled by default) BIP70 would realise that support
  had been completely removed in 0.20.0. However we should be able to
  remove it for 0.21.0.

ACKs for top commit:
  jnewbery:
    utACK c4ffcf0
  MarcoFalke:
    ACK c4ffcf0 with or without the "catch-all reject"

Tree-SHA512: a5dd4231ed97c9dd1984fb90d69a8725df2fdda0b963269b0575601c74528e5d820a4a863c428f8ede86eaae2a1606671fe1fcebdeb96b1023f7a5f899270284

Author: laanwj

configure.ac

@@ -229,16 +229,6 @@ AC_ARG_ENABLE([zmq],
   [use_zmq=$enableval],
   [use_zmq=yes])
 
-AC_ARG_ENABLE([bip70],
-  [AS_HELP_STRING([--enable-bip70],
-  [BIP70 (payment protocol) support in the GUI (no longer supported)])],
-  [enable_bip70=$enableval],
-  [enable_bip70=no])
-
-if test x$enable_bip70 != xno; then
-  AC_MSG_ERROR([BIP70 is no longer supported!])
-fi
-
 AC_ARG_WITH([libmultiprocess],
   [AS_HELP_STRING([--with-libmultiprocess=yes|no|auto],
   [Build with libmultiprocess library. (default: auto, i.e. detect with pkg-config)])],