remove unnecessary files from pypi source distribution (deepmodeling#2565)

Our PyPi source distribution package is over 30MB which is too large!
See https://pypi.org/project/deepmd-kit/2.2.2/#files
By default, when using `setuptools-scm`, all files will be added to the
package. This PR excludes directories that are not used for building and
installing, including:

- source/tests
- source/api_c/tests
- source/api_cc/tests
- source/lib/tests
- source/lmp/tests
- doc
- examples
- data
- .github

After removing these files from the source distribution, the package is
only 708 KB.

---------

Signed-off-by: Jinzhe Zeng <[email protected]>

Author: njzjz

MANIFEST.in

@@ -0,0 +1,9 @@
+prune source/tests
+prune source/api_c/tests
+prune source/api_cc/tests
+prune source/lib/tests
+prune source/lmp/tests
+prune doc
+prune examples
+prune data
+prune .github