Remove the unused _get_unused_flavor_id()

This patch removes the unused _get_unused_flavor_id() for the
maintainability.

Change-Id: I868c51c68d4ef1c73ea47f89e885d12602527e25
diff --git a/tempest/api/compute/admin/test_servers.py b/tempest/api/compute/admin/test_servers.py
index 1f2ddf4..49af645 100644
--- a/tempest/api/compute/admin/test_servers.py
+++ b/tempest/api/compute/admin/test_servers.py
@@ -14,7 +14,6 @@
 
 from tempest.api.compute import base
 from tempest.common.utils import data_utils
-from tempest import exceptions
 from tempest import test
 
 
@@ -44,16 +43,6 @@
                                               wait_until='ACTIVE')
         cls.s2_id = server['id']
 
-    def _get_unused_flavor_id(self):
-        flavor_id = data_utils.rand_int_id(start=1000)
-        while True:
-            try:
-                resp, body = self.flavors_client.get_flavor_details(flavor_id)
-            except exceptions.NotFound:
-                break
-            flavor_id = data_utils.rand_int_id(start=1000)
-        return flavor_id
-
     @test.attr(type='gate')
     def test_list_servers_by_admin(self):
         # Listing servers by admin user returns empty list by default
diff --git a/tempest/api/compute/v3/admin/test_servers.py b/tempest/api/compute/v3/admin/test_servers.py
index 579a535..366cfc6 100644
--- a/tempest/api/compute/v3/admin/test_servers.py
+++ b/tempest/api/compute/v3/admin/test_servers.py
@@ -14,7 +14,6 @@
 
 from tempest.api.compute import base
 from tempest.common.utils import data_utils
-from tempest import exceptions
 from tempest import test
 
 
@@ -44,16 +43,6 @@
                                               wait_until='ACTIVE')
         cls.s2_id = server['id']
 
-    def _get_unused_flavor_id(self):
-        flavor_id = data_utils.rand_int_id(start=1000)
-        while True:
-            try:
-                resp, body = self.flavors_client.get_flavor_details(flavor_id)
-            except exceptions.NotFound:
-                break
-            flavor_id = data_utils.rand_int_id(start=1000)
-        return flavor_id
-
     @test.attr(type='gate')
     def test_list_servers_by_admin(self):
         # Listing servers by admin user returns empty list by default