Remove unused template parameter

[quantumsteve]

Please review the developer documentation
on the wiki of this project that contains help and requirements.

Proposed changes

Describe what this PR changes and why. If it closes an issue, link to it here
with a supported keyword.

The member function VectorSoaContainer::copyIn has a template parameter T1 that in the current codebase is always equal to T. I see more risks than benefits to the additional functionality.

Found while working on #4684.

What type(s) of changes does this code introduce?

Delete the items that do not apply

• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Checklist

Update the following with a yes where the items apply. If you're unsure about any of them, don't hesitate to ask. This is
simply a reminder of what we are going to look for before merging your code.

• Yes. This PR is up to date with current the current state of 'develop'
• Yes. Code added or changed in the PR has been clang-formatted

[williamfgc]

Test this please