Don't check whether yaml responses are well-formed

pyyaml is unable to parse complex dictionary keys: say, a list or a
dictionary. See yaml/pyyaml#88

Tarantool however supports this kind of output:

 | tarantool> {[{k = 'v'}] = 1}
 | ---
 | - ? k: v
 |   : 1
 | ...

When such response is arrived to test-run, pyyaml raises 'found
unhashable key' exception and test-run reports it as '[Lost current
connection]'.

Let's consider 'core = tarantool' tests. There is no much need to verify
whether a tarantool answer is well-formed yaml document, because it
anyway will be verified against a result file. And also it is unable to
handle the case above. So the check is removed.

See tarantool/tarantool#4421

lib/admin_connection.py

@@ -24,8 +24,6 @@
 import re
 import sys
 
-import yaml
-
 from tarantool_connection import TarantoolConnection
 from tarantool_connection import TarantoolPool
 from tarantool_connection import TarantoolAsyncConnection
@@ -75,11 +73,8 @@ def cmd(self, socket, cmd, silent):
             if (res.rfind("\n...\n") >= 0 or res.rfind("\r\n...\r\n") >= 0):
                 break
 
-        try:
-            yaml.safe_load(res)
-        finally:
-            if not silent:
-                sys.stdout.write(res.replace("\r\n", "\n"))
+        if not silent:
+            sys.stdout.write(res.replace("\r\n", "\n"))
         return res