sanitizer_common: Remove Fuchsia support for reading flags from files

This has never really been used in practice.  Fuchsia is moving
away from the support this requires, so don't use it.

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D122500

Author: frobtech

compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp

@@ -386,29 +386,8 @@ void GetMemoryProfile(fill_profile_f cb, uptr *stats) {}
 
 bool ReadFileToBuffer(const char *file_name, char **buff, uptr *buff_size,
                       uptr *read_len, uptr max_len, error_t *errno_p) {
-  zx_handle_t vmo;
-  zx_status_t status = __sanitizer_get_configuration(file_name, &vmo);
-  if (status == ZX_OK) {
-    uint64_t vmo_size;
-    status = _zx_vmo_get_size(vmo, &vmo_size);
-    if (status == ZX_OK) {
-      if (vmo_size < max_len)
-        max_len = vmo_size;
-      size_t map_size = RoundUpTo(max_len, GetPageSize());
-      uintptr_t addr;
-      status = _zx_vmar_map(_zx_vmar_root_self(), ZX_VM_PERM_READ, 0, vmo, 0,
-                            map_size, &addr);
-      if (status == ZX_OK) {
-        *buff = reinterpret_cast<char *>(addr);
-        *buff_size = map_size;
-        *read_len = max_len;
-      }
-    }
-    _zx_handle_close(vmo);
-  }
-  if (status != ZX_OK && errno_p)
-    *errno_p = status;
-  return status == ZX_OK;
+  *errno_p = ZX_ERR_NOT_SUPPORTED;
+  return false;
 }
 
 void RawWrite(const char *buffer) {