Remove x86_64-linux-gnu-make-debug builder

Removing static-debug make builder because is not different from static
make. Moreover, the main compiler strategy for libwebm is cmake now.

Change-Id: I43059716a4ec09c4510f959553b4d7d1b3806947
Bug: b:185520494
Reviewed-on: https://chromium-review.googlesource.com/c/codecs/infra/+/3341780
Reviewed-by: James Zern <jzern@google.com>
Commit-Queue: Roberto Alanis Baez <alanisbaez@google.com>
4 files changed