Removed unused monotonic module

ebook_converter/utils/monotonic.py

@@ -1,10 +0,0 @@
-try:
-    from time import monotonic
-except ImportError:
-    from ebook_converter.constants_old 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