[xplat] remove -weak_framework (pytorch#89233)

Summary: The `-weak_framework` flag is no longer necessary, Buck will weakly link frameworks depending on the `target_sdk_version` of the binary being linked.

Test Plan:
Compare IG load commands before and after change with P553208168
```
load command difference in Instagram.app/Frameworks/InstagramXplatFramework.framework/InstagramXplatFramework
 --- /tmp/tmpvd97s2v0    2022-11-16 12:13:54.082910598 -0800
+++ /tmp/tmpj20r_4ca    2022-11-16 12:13:54.082910598 -0800
@@ -9,7 +9,7 @@
        /System/Library/Frameworks/CoreHaptics.framework/CoreHaptics (compatibility version 1.0.0, current version 1.0.0, weak)
        /System/Library/Frameworks/CoreImage.framework/CoreImage (compatibility version 1.0.0, current version 5.0.0)
        /System/Library/Frameworks/CoreLocation.framework/CoreLocation (compatibility version 1.0.0, current version 2780.0.17)
-       /System/Library/Frameworks/CoreML.framework/CoreML (compatibility version 1.0.0, current version 1.0.0, weak)
+       /System/Library/Frameworks/CoreML.framework/CoreML (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/CoreMedia.framework/CoreMedia (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/CoreServices.framework/CoreServices (compatibility version 1.0.0, current version 1226.0.0)
        /System/Library/Frameworks/CoreTelephony.framework/CoreTelephony (compatibility version 1.0.0, current version 0.0.0)
@@ -33,9 +33,9 @@
        /System/Library/Frameworks/Security.framework/Security (compatibility version 1.0.0, current version 60420.40.34)
        /System/Library/Frameworks/SystemConfiguration.framework/SystemConfiguration (compatibility version 1.0.0, current version 1241.40.2)
        /System/Library/Frameworks/UIKit.framework/UIKit (compatibility version 1.0.0, current version 6109.1.108)
-       /System/Library/Frameworks/UserNotifications.framework/UserNotifications (compatibility version 1.0.0, current version 1.0.0, weak)
+       /System/Library/Frameworks/UserNotifications.framework/UserNotifications (compatibility version 1.0.0, current version 1.0.0)
        /System/Library/Frameworks/VideoToolbox.framework/VideoToolbox (compatibility version 1.0.0, current version 1.0.0)
-       /System/Library/Frameworks/WebKit.framework/WebKit (compatibility version 1.0.0, current version 614.2.9, weak)
+       /System/Library/Frameworks/WebKit.framework/WebKit (compatibility version 1.0.0, current version 614.2.9)
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1319.0.0)
        /usr/lib/libbz2.1.0.dylib (compatibility version 1.0.0, current version 1.0.8)
        /usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1300.32.0)
```
Both these changes are correct, WebKit is available from 8.0, UserNotifications from 10.0 and CoreML from 11.0. Instagram has a deployment target of 12.4.

Reviewed By: ebgraham

Differential Revision: D41348639

Pull Request resolved: pytorch#89233
Approved by: https://github.com/malfet

c2_defs.bzl

@@ -221,26 +221,13 @@ def get_c2_fbobjc_ios_frameworks():
     frameworks = []
 
     if get_c2_mpscnn():
-        frameworks.append(
+        frameworks.extend([
             "$SDKROOT/System/Library/Frameworks/Metal.framework",
-        )
+            "$SDKROOT/System/Library/Frameworks/MetalPerformanceShaders.framework",
+        ])
 
     return frameworks
 
-def get_c2_fbobjc_linker_flags():
-    flags = []
-
-    if get_c2_mpscnn():
-        # Need linker flags as no platform_frameworks exist, and we can't
-        # use MPSCNN on x86_64.
-        # We use weak_framework as it's iOS 10
-        flags = [
-            "-L$SDKROOT/System/Library/Frameworks/MetalPerformanceShaders.framework",
-            "-weak_framework",
-            "MetalPerformanceShaders",
-        ]
-    return flags
-
 def get_c2_fbobjc_exported_preprocessor_flags():
     flags = []
 
@@ -311,12 +298,6 @@ def get_c2_default_cxx_args():
             STATIC_LIBRARY_IOS_CONFIG,
             extra_target_config = C2_FBOBJC_EXTRA_TARGET_CONFIG,
         ),
-        fbobjc_exported_platform_linker_flags = [
-            (
-                "iphoneos",
-                get_c2_fbobjc_linker_flags(),
-            ),
-        ],
         fbobjc_exported_platform_preprocessor_flags = [
             (
                 "iphoneos",