get rid of -ObjC linker flag

[incanus]

This flag is used in order to ensure that categories are properly linked into the final product. Another approach here would be add class methods to each category, then call them each from a non-category to ensure they get pulled in as linked dependencies.

https://developer.apple.com/library/mac/qa/qa1490/_index.html

Passing the -ObjC option to the linker causes it to load all members of static libraries that implement any Objective-C class or category. This will pickup any category method implementations. But it can make the resulting executable larger, and may pickup unnecessary objects. For this reason it is not on by default.

This will decrease our binary size.

[incanus]

Would love your 👀 here @1ec5, but I think this should just work.

[incanus]

👉 #2967

[incanus]

Implemented in 423cfc1.