Revert "[mlgo] Dependency-free training mode logger"

This reverts commit c5ff6f72.

This breaks building on macOS:

FAILED: lib/Analysis/CMakeFiles/LLVMAnalysis.dir/TensorSpec.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -DBUILD_EXAMPLES -DGTEST_HAS_RTTI=0 -D_DEBUG -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/clang-build/lib/Analysis -I/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/lib/Analysis -I/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/clang-build/include -I/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/include -fPIC -fvisibility-inlines-hidden -Werror=date-time -Werror=unguarded-availability-new -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -pedantic -Wno-long-long -Wc++98-compat-extra-semi -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported -fdiagnostics-color -O3 -DNDEBUG -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk -mmacosx-version-min=10.14  -fno-exceptions -fno-rtti -UNDEBUG -std=c++17 -MD -MT lib/Analysis/CMakeFiles/LLVMAnalysis.dir/TensorSpec.cpp.o -MF lib/Analysis/CMakeFiles/LLVMAnalysis.dir/TensorSpec.cpp.o.d -o lib/Analysis/CMakeFiles/LLVMAnalysis.dir/TensorSpec.cpp.o -c /Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/lib/Analysis/TensorSpec.cpp
In file included from /Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/lib/Analysis/TensorSpec.cpp:16:
In file included from /Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/include/llvm/Analysis/TensorSpec.h:16:
/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/include/llvm/Support/JSON.h:354:29: error: non-constant-expression cannot be narrowed from type 'unsigned long' to 'int64_t' (aka 'long long') in initializer list [-Wc++11-narrowing]
    create<int64_t>(int64_t{I});
                            ^
/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/lib/Analysis/TensorSpec.cpp:55:18: note: in instantiation of function template specialization 'llvm::json::Value::Value<unsigned long, void, void, void>' requested here
        OS.value(D);
                 ^
/Users/buildslave/jenkins/workspace/clang-stage1-cmake-RA-incremental/llvm-project/llvm/include/llvm/Support/JSON.h:354:29: note: insert an explicit cast to silence this issue
    create<int64_t>(int64_t{I});
                            ^
                            static_cast<int64_t>( )
1 error generated.

https://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-incremental/33120/consoleFull#-145995569149ba4694-19c4-4d7e-bec5-911270d8a58c