[InstSimplify] Fix the indentation throughout the interface header file.

The forward declarations and the SimplifyQuery class at the beginning of the namespace weren't indented. But the closing brace for SimplifyQuery and everything after it were indented.

This commit makes the whole file consistent to no identation per coding standards. The signature of every function in this file changed a few weeks ago so this isn't a big disturbance to the revision history.

llvm-svn: 303588