UI: Don't reserve signal vector size

[cg2121]

Description

In no other place in the program do we reserve the vector size when using them for signals. This creates an extra step if signals are added or removed.

Motivation and Context

One less extra step to worry about

How Has This Been Tested?

Ran OBS and everything still worked

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.