main/boost1.75: don't use custom statx implementation

When there is no statx function, but the statx syscall is detected,
boost-filesystem implements a statx function that directly calls the
syscall.

This is broken, because statx might not be implemented on the running
system, and there is no logic to fall back to fstatat.

Remove the build-time detection of the statx syscall, so that the code
falls back to `stat`.

Fixes #12349
7 jobs for !17410 with boost-fix-statx in 4 seconds
detached
Status Job ID Name Coverage
  Lint
canceled #303949
docker-alpine x86_64 allowed to fail
lint

00:00:04

 
  Build
canceled #303954
docker-alpine ci-build aarch64
build-aarch64

canceled #303955
docker-alpine ci-build armv7
build-armv7

canceled #303953
docker-alpine ci-build ppc64le
build-ppc64le

canceled #303952
docker-alpine ci-build s390x
build-s390x

canceled #303951
docker-alpine ci-build x86
build-x86

canceled #303950
docker-alpine ci-build x86_64
build-x86_64