Crawler: guppy plugin simplification

Since we now only load the guppy plugin when the user requested it, it's
better just to toss an import error if we can't load the guppy module.

plugins/guppy_plugin.py

@@ -2,23 +2,16 @@
 import csv
 import logging
 
-LOG = logging.getLogger("crawler")
+from guppy import hpy
 
-try:
-    from guppy import hpy
-    ACTIVE = True
-except:
-    LOG.debug('Guppy plugin not found. If you want memory profiling `pip install guppy`')
-    ACTIVE = False
+LOG = logging.getLogger("crawler")
 
 
 class Heap(Plugin):
     """
     Calculate heap consumed before and after request
     """
 
-    active = False
-
     def __init__(self, write_csv=False):
         super(Heap, self).__init__()
         self.heap_urls = self.data['heap_urls'] = {}