Use builtin monotonic in py3

src/calibre/constants.py

@@ -168,7 +168,6 @@ class Plugins(collections.Mapping):
                 'chm_extra',
                 'icu',
                 'speedup',
-                'monotonic',
                 'unicode_names',
                 'zlib2',
                 'html',
@@ -183,6 +182,10 @@ class Plugins(collections.Mapping):
                 'certgen',
                 'lzma_binding',
             ]
+        if not ispy3:
+            plugins.extend([
+                'monotonic',
+            ])
         if iswindows:
             plugins.extend(['winutil', 'wpd', 'winfonts'])
         if isosx:

src/calibre/utils/monotonic.py

@@ -1,9 +1,12 @@
 # vim:fileencoding=utf-8
 
-from calibre.constants import plugins
+try:
+    from time import monotonic
+except ImportError:
+    from calibre.constants import plugins
 
-monotonicp, err = plugins['monotonic']
-if err:
-    raise RuntimeError('Failed to load the monotonic module with error: ' + err)
-monotonic = monotonicp.monotonic
-del monotonicp, err
+    monotonicp, err = plugins['monotonic']
+    if err:
+        raise RuntimeError('Failed to load the monotonic module with error: ' + err)
+    monotonic = monotonicp.monotonic
+    del monotonicp, err