AbstractBytecodeArray was introduced in order to let the bytecode
array accessor work on either a Handle<BytecodeArray> or a serialized
BytecodeArrayRef. We have since implemented direct heap access for
bytecode arrays, so we can now remove the abstraction again.

Note that this means that as far as bytecode iteration is concerned
we no longer access the bytecode array through the BytecodeArrayRef.
I will remove the obsolete methods from that class in a follow-up CL.
The downside is the loss of this explicit interface. The upside is
simplicity and less code. We can justify the downside with the fact
that the bytecode array data is immutable and thus the Ref indirection
less meaningful than in other cases.

Bug: v8:7790
Change-Id: I0fe87b4efd0f77785f5a0917ab213c6031d9cc74
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2707166Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72955}