Revert "build: Split out mkfs in BuildImageMkfs"

This reverts commit 2b72b7f0.

out/target/product/generic_x86/installed-files.txt \${DIST_DIR}/installed-files-rescued.txt; exit 1 ) )" 
2018-11-08 19:12:28 - build_image.py - ERROR : Failed to build out/target/product/generic_x86/obj/PACKAGING/systemimage_intermediates/system.img from out/target/product/generic_x86/system 
Traceback (most recent call last): 
File "build/make/tools/releasetools/build_image.py", line 767, in <module> 
main(sys.argv[1:]) 
File "build/make/tools/releasetools/build_image.py", line 755, in main 
BuildImage(in_dir, image_properties, out_file, target_out) 
File "build/make/tools/releasetools/build_image.py", line 449, in BuildImage 
CheckHeadroom(mkfs_output, prop_dict) 
NameError: global name 'mkfs_output' is not defined 


Bug: 111302946
Reason for revert: Build problem

Change-Id: I786f232e07af653a7207509055df5a07a6d8bb9e