[IOS] Remove redundant fmt dependencies

[Saadnajmi]

Summary:

fmt is required by many different podspecs, but is only used by Folly. I verified this by removing fat altogether and seeing what build errors I got. Cocoapods supports transitive dependencies, so let's simplify the build graph a bit and mark fmt as only a dependency of folly.

Changelog:

[IOS] [CHANGED] - Remove redundant fmt dependencies

Test Plan:

CI should pass. Local build of RNTester works.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	19,495,291	+37
android	hermes	armeabi-v7a	n/a	--
android	hermes	x86	n/a	--
android	hermes	x86_64	n/a	--
android	jsc	arm64-v8a	22,867,570	+23
android	jsc	armeabi-v7a	n/a	--
android	jsc	x86	n/a	--
android	jsc	x86_64	n/a	--

Base commit: be09d12
Branch: main

[NickGerleman]

DoubleConversion is in this same boat, if we are able to make exported headers work nicely everywhere.

[Saadnajmi]

DoubleConversion is in this same boat, if we are able to make exported headers work nicely everywhere.

I can take a look. I was looking at cleaning up the header search paths too

[Saadnajmi]

@NickGerleman It looks I can remove the header search paths for fmt, and the dependency/header search paths for DoubleConversion too. One thing I'm not clear about is that I think codegen (which generates ReactCodegen.podspec.json) needs both, so I've left fat and DoubleConversion a dependency there. I'm not sure if it's fine for codegen to get the dependency through folly, or if it generates code that uses either library.

[Saadnajmi]

@NickGerleman I did some testing. Removing the fmt header search paths breaks dynamic frameworks support, since I guess most things depend on folly eventually. Removing the DoubleConversion dependency seems to be in the same boat. So I think the change in its current form is what works.