Remove the irrelevant prefix "I" from all the AST classes where it was present.
Now we have only three different consistent prefixes:
- "A" for language-independent classes
- "C" for C-specific classes
- "J" for Java-specific classes

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@14492 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c