Remove entries from `build_overrides/tint.gni`

The build_override file was setting the overrides to the same value as
the defaults. The existence of the entries in build_overrides was also
causing them to not be declared as arguments in the
tint_overrides_with_defaults.gni file. This then means that anything
that was in build_overrides/tint.gni could not be overridden with gn
args settings.

Change-Id: I0552958acec57aaad7cdcea7173321b60685613d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/147580
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>
Reviewed-by: James Price <jrprice@google.com>
Commit-Queue: Dan Sinclair <dsinclair@chromium.org>
diff --git a/build_overrides/tint.gni b/build_overrides/tint.gni
index 457b135..7d5af1a 100644
--- a/build_overrides/tint.gni
+++ b/build_overrides/tint.gni
@@ -15,10 +15,3 @@
 tint_spirv_tools_dir = "//third_party/vulkan-deps/spirv-tools/src"
 tint_spirv_headers_dir = "//third_party/vulkan-deps/spirv-headers/src"
 tint_glslang_dir = "//third_party/vulkan-deps/glslang/src"
-
-tint_build_spv_reader = true
-tint_build_spv_writer = true
-tint_build_wgsl_reader = true
-tint_build_wgsl_writer = true
-
-tint_build_unittests = true