[lit] Remove semicolons in Python code

Summary:
Semicolons aren't necessary as statement terminators in Python, and
each of these uses are superfluous as they appear at the end of a line.
The convention is to not use semicolons where not needed, so remove them.

Reviewers: echristo, delcypher, beanz, ddunbar

Subscribers: llvm-commits, mehdi_amini

Differential Revision: https://reviews.llvm.org/D25409

llvm-svn: 283707