remove Assembler::here()

It's just a shortcut for

   Assembler::Label l;
   a->label(&l);

and it never really took off.
It's easier to work on Label without it.

Change-Id: I4a060f78f235ac3fcc87b996f5d9404ffba43c53
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/288997
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Herb Derby <herb@google.com>
3 files changed