Revert "BUILD.gn: Make a better interface with dependents. (#1875)" (#1876)

This reverts commit 3cddf913.

This breaks the Chrome roll:

ERROR Unresolved dependencies.
//third_party/SPIRV-Tools/src/test/fuzzers:fuzzer_config(//build/toolchain/linux:clang_x64)
needs //third_party/SPIRV-Tools/src:spvtools_config(//build/toolchain/linux:clang_x64)
GN gen failed: 1