How to use functions in xtcio.h from third-party program with gromacs 2021.1

GROMACS version: 2021.1
GROMACS modification: No

I used gromacs 2019.2 and analyzed the trajectories by my own programs.
These programs call functions in xtcio.h to directly read xtc files.
In particular, I included GMXroot/include/gromacs/fileio/xtcio.h and linked the programs by -lgromacs.

Recently, I have tried to move to a newer version of gromacs,
and I realized that the xtcio.h file is there anymore.

Is there any way to use to the xtcio.h file and link my program with gromacs2021.1?

The file is there in my gmx 2021 tree.

I installed gromacs2021.2 again but I could not find the file under the installation directory,
but I found it in source tree.

Here is my installation script.

~/programs/cmake-3.21.0-rc2-linux-x86_64/bin/cmake ..  \
 -DCMAKE_INSTALL_PREFIX=~/programs/gromacs-2021.2/  \
make -j 10
make install -j 10

I checked files by

ls -p ~/programs/gromacs-2021.2/include/gromacs/

then I find only four directories,

math/  mdrun/  restraint/  utility/

On the other hand, I can find the following files under the installation directory of gromacs2019.2 (~/programs/gromacs-2019.2/include/gromacs/):

analysisdata/   fileio/         mdtypes/   restraint/   trajectoryanalysis/
analysisdata.h  gmxana/         options/   selection/   trajectoryanalysis.h
commandline/    gpu_utils/      options.h  selection.h  utility/
commandline.h   linearalgebra/  pbcutil/   timing/      utility.h
compat/         math/           random/    topology/    version.h
fft/            mdlib/          random.h   trajectory/

And I used the fileio/xtcio.h there previously.

Anyway, I found it in the source file, gromacs-2021.2/src/gromacs/fileio/, probably as hess meant.
Also, I was able to dynamically link my programs to the gromacs so files.

I would appreciate if someone could tell me whether the elimination from the installation directory was on purpose. (I just might have overlooked some comment in release notes, though.)

Many thanks.