Merge gtech_tool functionality into registry_tool

This change consolidates gtech_tool into registry_tool.  Since App Engine has
no actual ACLs on the remote API (any access is essentially root access), we're
removing this to avoid giving the impression to users that gtech_tool is truly
locked down from a security perspective compared to registry_tool.

In addition to merging GtechTool.COMMAND_MAP into RegistryTool.COMMAND_MAP, this
change also removes the {create,update}_sandbox_tld commands (which only made
sense for gtech_tool) and removes references to gtech_tool in the documentation.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=134828710

java/google/registry/tools/UniformRapidSuspensionCommand.java

@@ -181,7 +181,8 @@ final class UniformRapidSuspensionCommand extends MutatingEppToolCommand impleme
     if (undo) {
       return "";
     }
-    StringBuilder undoBuilder = new StringBuilder("UNDO COMMAND:\n\ngtech_tool -e ")
+    StringBuilder undoBuilder = new StringBuilder("UNDO COMMAND:\n\n)")
+        .append("registry_tool -e ")
         .append(RegistryToolEnvironment.get())
         .append(" uniform_rapid_suspension --undo --domain_name ")
         .append(domainName);