Revert patch adding support for logging the current role.

This reverts commit a8a8867912, committed
by me earlier today (2011-01-12).  This isn't safe inside an aborted
transaction.

Noted by Tom Lane.

doc/src/sgml/config.sgml

@@ -3504,12 +3504,7 @@ local0.*    /var/log/postgresql
             </row>
             <row>
              <entry><literal>%u</literal></entry>
-             <entry>Login user name</entry>
-             <entry>yes</entry>
-            </row>
-            <row>
-             <entry><literal>%U</literal></entry>
-             <entry>Current user name</entry>
+             <entry>User name</entry>
              <entry>yes</entry>
             </row>
             <row>

src/backend/utils/error/elog.c

@@ -1826,16 +1826,6 @@ log_line_prefix(StringInfo buf, ErrorData *edata)
 					appendStringInfoString(buf, username);
 				}
 				break;
-			case 'U':
-				if (MyProcPort)
-				{
-					const char *username = GetUserNameFromId(GetUserId());
-
-					if (username == NULL || *username == '\0')
-						username = _("[unknown]");
-					appendStringInfoString(buf, username);
-				}
-				break;
 			case 'd':
 				if (MyProcPort)
 				{