superpmi collections: do removeDup before clean phase

[BruceForstall]

superpmi.py and superpmicollect (unit test) both do collections in these phases:

1. collect .MC files
2. merge .MC files to .MCH
3. create a "clean" .MCH with no SuperPMI failures
4. remove dups in the .MCH file
5. create TOC file
6. test final .MCH file is clean

Swap steps 3 and 4: remove dups first, to avoid wasting time compiling the dups when creating the "clean" .MCH file.