Revert OnionTile direct dependency — use GPU_test project instead

OnionTile should not be a hard dependency of ESMFold.jl. GPU kernels are
loaded optionally via the GPU_test project environment.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: claudey

Project.toml

@@ -15,7 +15,6 @@ Mmap = "a63ad114-7e13-5084-954f-fe012c677804"
 NNlib = "872c559c-99b0-510c-b3b7-b6c96a88d5cd"
 NPZ = "15e1cf62-19b3-5cfa-8e77-841668bca605"
 Onion = "fdebf6c2-71da-43a1-b539-c3bc3e09c5c6"
-OnionTile = "a1b2c3d4-e5f6-7890-abcd-ef1234567890"
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 cuDNN = "02a925ec-e4fe-4b08-9a7e-0d78e3d38ccd"