Revert "[vm, compiler] Unwind record alignment."

This reverts commit b91dcdf.

Reason for revert: Broke g3 Windows cross compilation.
`unwinding_records_win.cc: 80: error: Failed to add growable function table: 0xc0000095`
https://ci.chromium.org/ui/p/dart/builders/ci.sandbox/google/42584/overview

Original change's description:
> [vm, compiler] Unwind record alignment.
>
> TEST=vm/dart/in_memory_elf_test
> Bug: #54206
> Change-Id: I3a0e15ee3f3b98602cd2cf8921f0334539e64a17
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/339225
> Reviewed-by: Alexander Aprelev <[email protected]>
> Commit-Queue: Ryan Macnak <[email protected]>

Bug: #54206
Change-Id: I8b57862f53af254040d0425e78abab0e608e33e7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/339942
Reviewed-by: Martin Kustermann <[email protected]>
Commit-Queue: Daco Harkes <[email protected]>
Bot-Commit: Rubber Stamper <[email protected]>
Reviewed-by: Ivan Inozemtsev <[email protected]>

runtime/bin/elf_loader.cc

@@ -92,11 +92,12 @@ class MemoryMappable : public Mappable {
       auto* memory = VirtualMemory::Allocate(
           map_size, type == File::kReadExecute, "dart-compiled-image");
       if (memory == nullptr) return nullptr;
-      result = new MappedMemory(memory->address(), length);
+      result = new MappedMemory(memory->address(), memory->size());
       memory->release();
       delete memory;
     } else {
-      result = new MappedMemory(start, length, /*should_unmap=*/false);
+      result = new MappedMemory(start, map_size,
+                                /*should_unmap=*/false);
     }
 
     size_t remainder = 0;