Standards checklist:

• The PR title is descriptive.
• The PR doesn't replicate another PR which is already open.
• I have read the contribution guide and followed all the instructions.
• The code follows the code style guide detailed in the wiki.
• The code is mine or it's from somewhere with an MIT-compatible license.
• The code is efficient, to the best of my ability, and does not waste computer resources.
• The code is stable and I have tested it myself, to the best of my abilities.
• If the code introduces new aliases, I provide a valid use case for all plugin users down below.

Changes:

• Remove deprecated git pull --rebase aliases
• Start deprecating ggpull/ggpur/ggpush for their alternative functions
• Start deprecating current_branch function in favor of what's in core
• Update README to reflect above changes and undocument some long-removed aliases

• Closes/supercedes Cleanup git aliases #9544
• Closes/supercedes Fix(git): remove duplicate alias for git pull rebase (Fixes #11104) #11227

Other comments:

I'm gonna be honest, I only wanted to just be able to use gup without unalias-ing it first in my zshrc. But the code for deprecation warnings seemed like a waste to just remove, and after taking a look it felt like some parts needed updates too, so why not make use of it so we can proceed with a system where we can actually transition functionalities from soft deprecation to removal? Some of these have been sitting here for a while now, after all (>2 years). Appreciate any feedback/conversation regarding this.