Remove build option firmware size impacts from rules.mk

[fauxpark]

For example:

...
BOOTMAGIC_ENABLE = no    # Virtual DIP switch configuration(+1000)
MOUSEKEY_ENABLE = yes    # Mouse keys(+4700)
EXTRAKEY_ENABLE = yes    # Audio control and System control(+450)
...

These numbers are misleading, because they are outdated and as @drashna mentioned here: #5485 (comment), dependent on the compiler version. It seems there is not much point having them around since they will simply never be accurate.

But... these are in every rules.mk, so I won't bother making a PR for this, even though I strongly feel these kinds of changes should be done sooner rather than later as QMK grows in popularity, complexity and size.

[drashna]

@jackhumbert @skullydazed

Personally, I'm in favor of this. They're not accurate, and I don't think we should keep them in the repo.

[noroadsleft]

Strongly in favor.

[roguepullrequest]

Would this z

[fauxpark]

Would this z

Probably not.