Audit content for unnecessary semicolons

[gcapes]

Semicolons at the end of a line suppress output from a command. However, there are multiple instances of this being used after disp where the command's only job is to print some output, and after plotting commands. In neither case does the semicolon serve a purpose, so I propose only using them after e.g. variable assignments.

I'll submit a PR, but after the current ones have been merged so things don't get too confusing.