Remove preprocess xplat build (#5801)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/5801

Fix the error
```
BUILD FAILED
Error running analysis for `fbsource//xplat/executorch/backends/qualcomm:preprocess (cfg:linux-x86_64-fbcode-platform010-clang15-no-san#5d1c5fc41fddc9ad)`

Caused by:
    0: Error in configured node dependency, dependency chain follows (-> indicates depends on, ^ indicates same configuration as previous):
              fbsource//xplat/executorch/backends/qualcomm:preprocess (cfg:linux-x86_64-fbcode-platform010-clang15-no-san#5d1c5fc41fddc9ad)
           -> fbsource//xplat/executorch/backends/qualcomm/passes:passes (^)

    1: looking up unconfigured target node `fbsource//xplat/executorch/backends/qualcomm/passes:passes`
    2: Error loading targets in package `fbsource//xplat/executorch/backends/qualcomm/passes` for target `fbsource//xplat/executorch/backends/qualcomm/passes:passes`
    3: package `fbsource//xplat/executorch/backends/qualcomm/passes:` does not exist
           missing `BUCK` file (also missing alternatives `BUCK.v2`, `BUCK`)
```
In https://www.internalfb.com/sandcastle/workflow/941252322124876986/artifact/actionlog.941252322206237690.stdout.1?selectedLines=622-633-1-77

Reviewed By: SS-JIA

Differential Revision: D63587929

fbshipit-source-id: 3fdf0065417b41f58966b08d01a1a19c2451fa9c