Match ccache functions in krb5.h with export list

Match ccache functions in krb5.h with export list

Commit 6e83d0bd31721ac86003530dd2450221dd05d0c2 (part of release 1.7)
added new ccache functions to krb5.h, but not to either export list.
Though commit ad5aa12f13aad7ec4cafcffeec4f2e84e56c9c78 exported
krb5_cc_move(), the rest remain unexported.

krb5_cc_lock(), krb5_cc_unlock(), krb5_cccol_lock(), and
krb5_cccol_unlock() are used internally, so remove them from krb5.h
and rename them to k5_cc_lock(), k5_cc_unlock(), k5_cccol_lock(), and
k5_cccol_unlock() respectively.

krb5_cccol_last_change_time() is not used, so remove it.

krb5_cc_last_change_time() is also not used, so remove it as well.
Update ccache interface to reflect removal.  Of particular note, this
function didn't behave as documented for KCM or KEYRING ccaches at
time of removal.

ticket: 7765