HOST_OUT_EXECUTABLES path is not needed in misc_info file

HOST_OUT_EXECUTABLES is already added to the PATH variable,
so it is not needed to add the path info for binaries in
misc_info.txt and <partition>_image_info.txt.

Earlier the mkuserimg item in the build_image dictionary is
hardcoded to "mkuserimg.sh", but now it is customized for
mkuserimg.sh and mkuserimg_mke2fs.sh, and maintained in
dictionary "ext_mkuserimg=$(MKEXTUSERIMG)" in misc_info.txt
and <partition>_image_info.txt, where it is used in the
build_image script while creating the images.

The problem here is the value for this key is set to build
path of the file mkuserimg file
$(HOST_OUT_EXECUTABLES)/mkuserimg.sh,
i.e. out/host/linux_x86/bin/mkuserimg.sh,
there by standalone signing the images using otatools is
not working as the executables are packed in bin folder.

Test: tools/releasetools/sign_target_files_apks
    -p <extracted ota-tools.zip folder>
    --extra_signapk_args=-f /etc/opt/cert_data.dat
    -v
    --replace_verity_private_key ~/build/target/product/security/verity
    --replace_verity_public_key ~/build/target/product/security/verity.x509.pem
    -k <key maping>
    <input target files zip>
    <output target files zip>

Change-Id: I57af1025ec38f3794f779c49faa0bf965afc6a5d