Dedup checksum calculation routines

I introduced a separate routine to cacluate checksum for ScriptGroup
in my previous CL, in addition to the one we use for regular scripts.
This CL removes the new one and uses the old one.

While I am on it, I made some other minor changes, e.g., changing
mBuildChecksum in RsdCpuScriptIml from char* to uint32_t, and a few
other minor cleanups in ScriptGroup2 implementation.

Change-Id: I168fdbb4e7bd14f1549a687e7b0d0ca6dd4da866
6 files changed