Makefile: remove workaround for jimtcl 0.80

Makefile: remove workaround for jimtcl 0.80

Commit 266a945ad3e8 ("jimtcl: update to version 0.80 (2020-10-29)")
adds a workaround to permit 'make distcheck' with jimtcl 0.80.
This has been fixed in jimtcl with commit d224c9a2b7b2 ("Makefile:
remove examples.api/Makefile while 'distclean'").

By using jimtcl from latest master branch, the workaround is not
required anymore.

Remove the workaround.

Change-Id: I10d91371b5a89d2a3c8599bce766f97eac44f0d9
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6227
Tested-by: jenkins
Reviewed-by: Oleksij Rempel <linux@rempel-privat.de>