e2fsprogs: clean up build dependencies

The E2FSPROGS_NEW_FILES variable captures all the files in the
e2fsprogs directory that are more recent than the
$(E2FSPROGS_BUILD_STAMP) stamp.

Unfortunately the e2fsprogs-install target creates a few files in the
build directory, thus making the e2fsprogs-build target out of date.

This patch removes those e2fsprogs-install build products from the
E2FSPROGS_NEW_FILES list.