* [RELAY] Move frontend utils

The util file currently under frontend is used from
outside of frontend (in qnn/op/legalizations). This suggests
that the file should be pushed up to a higher level.

The benefit from this change is that importing qnn no longer
also imports all the frontends.

* Inline get_scalar_from_constant

Change-Id: I1cc64e9ecb0eadb6ac0f7b62e6ea174644af4ad4

* Remove util.py from Relay

Change-Id: If9cd7cf3fc0bd1861a3a9b5604f338e084d8db96

* Shorten functions

Change-Id: Ieb537d82e6ee52421ff05a90cd00a03679ffebf2

* Line length

Change-Id: I1d216b7e73a060c4f118f5da50ce58b18eba907f