#1156 Removed dead code in ToolDef type checker and interpreter

• Best to review per commit.
• No end-user visible changes.
• Changes:
  • ToolDefExec.assign(Expression, ...) computes childTypes, but doesn't use it. Removed that code.
  • ToolInvokeChecker.tchecker doesn't use its hints parameter. Removed it, and in some of its callers as well.

Closes #1156 (closed)