Bazel: Remove exporter_tool CheckCurrent method.

CheckCurrent() was intended to verify more than the out-of-date
checks done by generate_gni. These turned out to be unnecessary
so removing CheckCurrent() as it adds nothing beyond what
is currently done by the generate_gni check in the Makefile.

Bug: skia:13485
Change-Id: I11fd9c13cba9578765356c01ecc3aeb71758f2fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/612258
Commit-Queue: Chris Mumford <cmumford@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
8 files changed