Remove unused gru imports

Neither of these files use the gru module anymore. I've tested that they 
work correctly after removing the unused imports.

Author: argilo

gnuradio-runtime/examples/mp-sched/wfm_rcv_pll_to_wav.py

@@ -8,7 +8,7 @@
 #
 #
 
-from gnuradio import gr, gru, eng_notation, filter
+from gnuradio import gr, eng_notation, filter
 from gnuradio import audio
 from gnuradio import analog
 from gnuradio import blocks

gr-digital/python/digital/crc.py

@@ -7,7 +7,6 @@
 #
 #
 
-from gnuradio import gru
 from . import digital_python as digital
 import struct