Drop dependency on monotonic

Since it's no longer used we can stop requiring it.
This also fixes the requirements check job after
change Ib8c1bf08f5fa7463911602b0df19315907c81e04.

Change-Id: I2f165999fbcc208067a265a3bba049fc86943a47

glance/common/timeutils.py

@@ -20,7 +20,6 @@ Time related utilities and helper functions.
 import datetime
 
 import iso8601
-from monotonic import monotonic as now  # noqa
 from oslo_utils import encodeutils
 
 # ISO 8601 extended time format with microseconds

lower-constraints.txt

@@ -52,7 +52,6 @@ Mako==1.0.7
 MarkupSafe==1.0
 mccabe==0.2.1
 mock==2.0.0
-monotonic==0.6
 mox3==0.25.0
 msgpack==0.5.6
 netaddr==0.7.19

requirements.txt

@@ -55,4 +55,3 @@ cursive>=0.2.1 # Apache-2.0
 
 # timeutils
 iso8601>=0.1.11 # MIT
-monotonic>=0.6 # Apache-2.0