[PP-1] Cleanup gd/Rotate::execute() arguments array overloading

Problem/Motivation

Follow-up to #2464023-34: Move GD-specific code from Rotate::validateArguments() to Rotate::execute() →

The arguments array doesn't need to be overloaded. Local variables can simply be used, since the arg changes are not passed on anywhere outside execute().

Proposed resolution

Something like reverse applying interdiff.2464023.32a.32b.txt →

Note git diff --color-words will be helpful for reviewers.

Remaining tasks

User interface changes

No.

API changes

No.

Data model changes

No.