chore: remove redundant @available checks (#34407)

* chore: require macOS 10.13 for Chromium

* chore: fix lint

shell/browser/mac/electron_application_delegate.mm

@@ -19,30 +19,6 @@
 
 #import <UserNotifications/UserNotifications.h>
 
-#if BUILDFLAG(USE_ALLOCATOR_SHIM)
-// On macOS 10.12, the IME system attempts to allocate a 2^64 size buffer,
-// which would typically cause an OOM crash. To avoid this, the problematic
-// method is swizzled out and the make-OOM-fatal bit is disabled for the
-// duration of the original call. https://crbug.com/654695
-static base::mac::ScopedObjCClassSwizzler* g_swizzle_imk_input_session;
-@interface OOMDisabledIMKInputSession : NSObject
-@end
-@implementation OOMDisabledIMKInputSession
-- (void)_coreAttributesFromRange:(NSRange)range
-                 whichAttributes:(long long)attributes  // NOLINT(runtime/int)
-               completionHandler:(void (^)(void))block {
-  // The allocator flag is per-process, so other threads may temporarily
-  // not have fatal OOM occur while this method executes, but it is better
-  // than crashing when using IME.
-  base::allocator::SetCallNewHandlerOnMallocFailure(false);
-  g_swizzle_imk_input_session->InvokeOriginal<
-      void, NSRange, long long, void (^)(void)>(  // NOLINT(runtime/int)
-      self, _cmd, range, attributes, block);
-  base::allocator::SetCallNewHandlerOnMallocFailure(true);
-}
-@end
-#endif  // BUILDFLAG(USE_ALLOCATOR_SHIM)
-
 static NSDictionary* UNNotificationResponseToNSDictionary(
     UNNotificationResponse* response) API_AVAILABLE(macosx(10.14)) {
   // [response isKindOfClass:[UNNotificationResponse class]]
@@ -109,16 +85,6 @@ static NSDictionary* UNNotificationResponseToNSDictionary(
 
   electron::Browser::Get()->DidFinishLaunching(
       electron::NSDictionaryToDictionaryValue(notification_info));
-
-#if BUILDFLAG(USE_ALLOCATOR_SHIM)
-  // Disable fatal OOM to hack around an OS bug https://crbug.com/654695.
-  if (base::mac::IsOS10_12()) {
-    g_swizzle_imk_input_session = new base::mac::ScopedObjCClassSwizzler(
-        NSClassFromString(@"IMKInputSession"),
-        [OOMDisabledIMKInputSession class],
-        @selector(_coreAttributesFromRange:whichAttributes:completionHandler:));
-  }
-#endif
 }
 
 - (void)applicationDidBecomeActive:(NSNotification*)notification {