gdbsupport: remove unnecessary `#ifndef IN_PROCESS_AGENT`

I suppose this code was copied from GDBserver and this ifndef was left
there.  As far as I know, IN_PROCESS_AGENT will never be defined when
building this file, so we can remove this.

Change-Id: I84fc408e330b3a29106df830a09342861cadbaf6

gdbsupport/tdesc.cc

@@ -400,7 +400,6 @@ void print_xml_feature::visit (const tdesc_reg *r)
 
 void print_xml_feature::visit_pre (const target_desc *e)
 {
-#ifndef IN_PROCESS_AGENT
   add_line ("<?xml version=\"1.0\"?>");
   add_line ("<!DOCTYPE target SYSTEM \"gdb-target.dtd\">");
   add_line ("<target>");
@@ -418,7 +417,6 @@ void print_xml_feature::visit_pre (const target_desc *e)
   for (const auto &c : compatible_list)
     add_line ("<compatible>%s</compatible>",
 	      tdesc_compatible_info_arch_name (c));
-#endif
 }
 
 void print_xml_feature::visit_post (const target_desc *e)