Switch platform WebRTC copts to defines so dependencies of it don't need to also specify the flag.

PiperOrigin-RevId: 495798557

internal/platform/implementation/BUILD

@@ -98,12 +98,6 @@ cc_library(
     hdrs = [
         "platform.h",
     ],
-    copts = select({
-        "@platforms//cpu:arm": [
-            "-DNO_WEBRTC",
-        ],
-        "//conditions:default": [],
-    }),
     defines = ["NO_WEBRTC"],
     visibility = [
         "//connections/implementation:__subpackages__",

internal/platform/implementation/ios/BUILD

@@ -42,12 +42,6 @@ objc_library(
         "utils.h",
         "wifi_lan.h",
     ],
-    copts = select({
-        "@platforms//cpu:arm": [
-            "-DNO_WEBRTC",
-        ],
-        "//conditions:default": [],
-    }),
     features = ["-layering_check"],
     deps = [
         ":Platform_cc",