Remove now-unused gni imports

Change-Id: I6c0e71cc40b9b5a46d29483aea382c2589c903ea
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/55668
Tested-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 8cd9cba..dafc50d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -12,10 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import("//build/config/c++/c++.gni")
 import("//build/config/compiler/compiler.gni")
-import("//build/config/mips.gni")
-import("//build/config/sysroot.gni")
 import("src/Reactor/reactor.gni")
 
 config("swiftshader_config") {