Revert unnecessary and incorrect change made to GraphWriter

Summary:
As pointed out in https://github.com/llvm/llvm-project/issues/52610, the
changes to GraphWriter made in https://reviews.llvm.org/D87202 introduced
some bad code and the changes are actually unnecessary for
-print-changed=dot-cfg. The code in question is guarded by a call to
DefaultDOTGraphTraits::hasEdgeDestLabels() which is always false when the
graph writer is called for -print-changed=dot-cfg. Revert this section of
the changes.

Author: Jamie Schmeiser <schmeise@ca.ibm.com>
Reviewed By:jrtc27(Jessica Clarke), xgupta(Shivam Gupta)
Differential Revision: https://reviews.llvm.org/D115649