Revert of [snapshot] Move builtins generation into mksnapshot (patchset #8 id:160001 of https://codereview.chromium.org/2760233005/ )

Reason for revert:
I think that this CL breaks chromium compilation on windows with clang (). All other CLs in the list looks trivial and don't change test/unittest/BUILD.gn.

[42456/47924] CXX obj/v8/test/unittests/unittests/value-serializer-unittest.obj
[42457/47924] LINK unittests.exe unittests.exe.pdb
FAILED: unittests.exe unittests.exe.pdb
E:/b/depot_tools/python276_bin/python.exe ../../build/toolchain/win/tool_wrapper.py link-wrapper environment.x64 False link.exe /nologo /OUT:./unittests.exe /PDB:./unittests.exe.pdb @./unittests.exe.rsp
bitmap-unittest.obj : error LNK2019: unresolved external symbol "public: void __cdecl v8::internal::List<class v8::internal::AllocationObserver *,class v8::internal::FreeStoreAllocationPolicy>::Add(class v8::internal::AllocationObserver * const &,class v8::internal::FreeStoreAllocationPolicy)" (?Add@?$List@PEAVAllocationObserver@internal@v8@@VFreeStoreAllocationPolicy@23@@internal@v8@@QEAAXAEBQEAVAllocationObserver@23@VFreeStoreAllocationPolicy@23@@Z) referenced in function "public: virtual void __cdecl v8::internal::Space::AddAllocationObserver(class v8::internal::AllocationObserver *)" (?AddAllocationObserver@Space@internal@v8@@UEAAXPEAVAllocationObserver@23@@Z)

slot-set-unittest.obj : error LNK2001: unresolved external symbol "public: void __cdecl v8::internal::List<class v8::internal::AllocationObserver *,class v8::internal::FreeStoreAllocationPolicy>::Add(class v8::internal::AllocationObserver * const &,class v8::internal::FreeStoreAllocationPolicy)" (?Add@?$List@PEAVAllocationObserver@internal@v8@@VFreeStoreAllocationPolicy@23@@internal@v8@@QEAAXAEBQEAVAllocationObserver@23@VFreeStoreAllocationPolicy@23@@Z)

bitmap-unittest.obj : error LNK2019: unresolved external symbol "public: bool __cdecl v8::internal::List<class v8::internal::AllocationObserver *,class v8::internal::FreeStoreAllocationPolicy>::RemoveElement(class v8::internal::AllocationObserver * const &)" (?RemoveElement@?$List@PEAVAllocationObserver@internal@v8@@VFreeStoreAllocationPolicy@23@@internal@v8@@QEAA_NAEBQEAVAllocationObserver@23@@Z) referenced in function "public: virtual void __cdecl v8::internal::Space::RemoveAllocationObserver(class v8::internal::AllocationObserver *)" (?RemoveAllocationObserver@Space@internal@v8@@UEAAXPEAVAllocationObserver@23@@Z)

slot-set-unittest.obj : error LNK2001: unresolved external symbol "public: bool __cdecl v8::internal::List<class v8::internal::AllocationObserver *,class v8::internal::FreeStoreAllocationPolicy>::RemoveElement(class v8::internal::AllocationObserver * const &)" (?RemoveElement@?$List@PEAVAllocationObserver@internal@v8@@VFreeStoreAllocationPolicy@23@@internal@v8@@QEAA_NAEBQEAVAllocationObserver@23@@Z)

./unittests.exe : fatal error LNK1120: 2 unresolved externals

Original issue's description:
> [snapshot] Move builtins generation into mksnapshot
>
> and out of the main library. This saves about 5% of binary size
> (800KB on x64, 373KB on android_arm).
>
> Only the GN build is supported; the GYP build is maintained working
> but does not support the feature.
>
> BUG=v8:6055
> CQ_INCLUDE_TRYBOTS=master.tryserver.v8:v8_linux_nosnap_rel;
>
> Review-Url: https://codereview.chromium.org/2760233005
> Cr-Commit-Position: refs/heads/master@{#44412}
> Committed: https://chromium.googlesource.com/v8/v8/+/4782bc0df89ceb127e38017b8dcf531222a0e966

TBR=jgruber@chromium.org,rmcilroy@chromium.org,machenbach@chromium.org,jkummerow@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:6055

Review-Url: https://codereview.chromium.org/2803903002
Cr-Commit-Position: refs/heads/master@{#44422}