Move cc_mutex code from k5-int.h - where it is globally available to cc-int.h

Move cc_mutex code from k5-int.h - where it is globally available to cc-int.h
where it is declared and used.  The functions are not exported by the library -
nor are they used outside lib/krb5/ccache...  For cc_file.h - include cc-int.h.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@21205 dc483132-0cff-0310-8789-dd5450dbe970