[InstrProf] Move BPFunctionNode test to ProfileDataTests

In https://reviews.llvm.org/D147812 I created
`BalancedPartitioningTest.cpp` and inadvertently drastically increased the
number of files needed to compile `SupportTests`. Instead lets move the
`BPFunctionNode` test to `unittests/ProfileData` so we can remove the
extra dependency.

Reviewed By: thakis

Differential Revision: https://reviews.llvm.org/D152325