Revert "3.0.x - radeapclient - parallel mode (and more stuff)"

This reverts commit 8d3601908a437f3580aa90dee052103cde093e06.
Parallel radeapclient patch - partial commit 1

Parallel radeapclient patch - partial commit 1:
New structures and global variables to handle files, request contexts,
statistics.
New functions to handle files and request contexts.
(Those are not called in this commit.)