setup.py: remove sensors from extras_require

setuptools doesn't like it.

README.rst

@@ -134,6 +134,7 @@ features (like the Web interface, exports modules, sensors...):
 .. code-block:: console
 
     pip install glances[action,batinfo,browser,cpuinfo,chart,docker,export,folders,gpu,ip,raid,snmp,web,wifi]
+    pip install https://bitbucket.org/gleb_zhulik/py3sensors/get/tip.zip
 
 To upgrade Glances to the latest version:
 

setup.py

@@ -90,7 +90,6 @@ setup(
         'gpu': ['nvidia-ml-py'],
         'ip': ['netifaces'],
         'raid': ['pymdstat'],
-        'sensors': ['https://bitbucket.org/gleb_zhulik/py3sensors/get/tip.zip'],
         'snmp': ['pysnmp'],
         'web': ['bottle', 'requests'],
         'wifi': ['wifi']