linker: simplify how warnings turn into errors past a certain api level.

This was motivated by the fact that most of the _anchors_ on the doc page were outdated. I've taken the simple expedient of removing those. I was then struck by the amount of copy & paste involved in showing both warning and error, so the new function takes care of that.

Change-Id: I82d3e6a6d8235a78f7cfe427b1209a1f9c83f682
diff --git a/linker/linker_globals.h b/linker/linker_globals.h
index 2bfdccd..e6b4bc6 100644
--- a/linker/linker_globals.h
+++ b/linker/linker_globals.h
@@ -28,6 +28,8 @@
 
 #pragma once
 
+#include "linker_debug.h"
+
 #include <link.h>
 #include <stddef.h>
 
@@ -49,7 +51,7 @@
       async_safe_format_fd(2, "\n"); \
     } while (false)
 
-void DL_WARN_documented_change(int api_level, const char* doc_link, const char* fmt, ...);
+bool DL_ERROR_AFTER(int target_sdk_version, const char* fmt, ...);
 
 #define DL_ERR_AND_LOG(fmt, x...) \
   do { \