We unconditionally link to $angle_spirv_tools_dir:spvtools_val, but we
only use SPIR-V validation with ASSERTs. This CL removes this
dependency when ASSERTs are disabled.

Bug: angleproject:4887
Test: CQ
Change-Id: Ic403b78196ecd895e4a0cdefb54ab4497651ccac
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2375872
Commit-Queue: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>