Remove workarounds for check_podspecs needed for older version of Cocoapods (#5724)

CI has been updated to Cocoapods 1.13, which fixes previous issues with the plugin_lint_mac test. Remove workarounds added previously.

See flutter/flutter#125812.

Author: vashworth

script/tool/lib/src/podspec_check_command.dart

@@ -142,9 +142,6 @@ class PodspecCheckCommand extends PackageLoopingCommand {
       podspecPath,
       '--configuration=Debug', // Release targets unsupported arm64 simulators. Use Debug to only build against targeted x86_64 simulator devices.
       '--skip-tests',
-      // TODO(vashworth): remove allow-warnings when https://github.com/flutter/flutter/issues/125812 is fixed.
-      // https://github.com/flutter/flutter/issues/125812
-      '--allow-warnings',
       '--use-modular-headers', // Flutter sets use_modular_headers! in its templates.
       if (libraryLint) '--use-libraries'
     ];

script/tool/test/podspec_check_command_test.dart

@@ -143,7 +143,6 @@ void main() {
                     .path,
                 '--configuration=Debug',
                 '--skip-tests',
-                '--allow-warnings',
                 '--use-modular-headers',
                 '--use-libraries'
               ],
@@ -159,7 +158,6 @@ void main() {
                     .path,
                 '--configuration=Debug',
                 '--skip-tests',
-                '--allow-warnings',
                 '--use-modular-headers',
               ],
               packagesDir.path),
@@ -201,7 +199,6 @@ void main() {
                     .path,
                 '--configuration=Debug',
                 '--skip-tests',
-                '--allow-warnings',
                 '--use-modular-headers',
                 '--use-libraries'
               ],
@@ -217,7 +214,6 @@ void main() {
                     .path,
                 '--configuration=Debug',
                 '--skip-tests',
-                '--allow-warnings',
                 '--use-modular-headers',
               ],
               packagesDir.path),