Port used limits to core API

Extension 'used limits' was extending core 'limits' API with used
resources information. So, provide such information in core API and
remove extension completely.
It does not require neither update of API router nor bump of
microversion.

Partially implements bp ext-to-core

Change-Id: I0ff71fbd0281eb2e34a9acbfc72ff8c14390e8d9
diff --git a/manila_tempest_tests/tests/api/test_limits.py b/manila_tempest_tests/tests/api/test_limits.py
index 044d601..5046b30 100644
--- a/manila_tempest_tests/tests/api/test_limits.py
+++ b/manila_tempest_tests/tests/api/test_limits.py
@@ -35,10 +35,12 @@
             "maxTotalShares",
             "maxTotalShareSnapshots",
             "maxTotalShareNetworks",
+            "maxTotalSnapshotGigabytes",
             "totalSharesUsed",
             "totalShareSnapshotsUsed",
             "totalShareNetworksUsed",
             "totalShareGigabytesUsed",
+            "totalSnapshotGigabytesUsed",
         ]
         [self.assertIn(key, limits["absolute"].keys()) for key in abs_keys]
 
@@ -54,7 +56,9 @@
         self.assertGreater(int(abs_l["maxTotalShares"]), -2)
         self.assertGreater(int(abs_l["maxTotalShareSnapshots"]), -2)
         self.assertGreater(int(abs_l["maxTotalShareNetworks"]), -2)
+        self.assertGreater(int(abs_l["maxTotalSnapshotGigabytes"]), -2)
         self.assertGreater(int(abs_l["totalSharesUsed"]), -2)
         self.assertGreater(int(abs_l["totalShareSnapshotsUsed"]), -2)
         self.assertGreater(int(abs_l["totalShareNetworksUsed"]), -2)
         self.assertGreater(int(abs_l["totalShareGigabytesUsed"]), -2)
+        self.assertGreater(int(abs_l["totalSnapshotGigabytesUsed"]), -2)