Simplify syntax test

cpanfile

@@ -18,5 +18,4 @@ requires "File::Copy::Recursive";
 requires "Moo", ">= 2.0";
 
 test_requires "Test::MockModule";
-test_requires "Test2::AsyncSubtest";
 test_requires "Test::Strict";

t/syntax.t

@@ -11,42 +11,12 @@ use FindBin qw/$Bin/;
 use POSIX qw( waitpid WNOHANG );
 use Time::HiRes qw( sleep );
 
+# Check syntax, use strict and use warnings on all perl files
+
 local $Test::Strict::TEST_WARNINGS = 1;
 
 my @dirs  = ('t', 'bin', "$Bin/../share/shutter/resources/modules/");
-my @files = Test::Strict::_all_perl_files(@dirs);
-
-run_parallel_tests(
-  4,
-  [
-    map {
-      my $file = $_;
-      sub { all_perl_files_ok($file); };
-    } @files
-  ],
-  "Syntax and strict checks for @dirs"
-);
-
-sub run_parallel_tests {
-  my ($MAX_JOBS, $tests, $name) = @_;
-
-  my $ast = Test2::AsyncSubtest->new(name => $name);
-
-  my @tests = @{$tests || []};
-
-  my %children;
-
-  while (@tests) {
-    if (keys %children < $MAX_JOBS) {
-      my $pid = $ast->run_fork(shift @tests);
-      $children{$pid}++;
-    }
-    waitpid($_, WNOHANG) && delete $children{$_} for keys %children;
-
-    last if !@tests;
-    sleep 0.01;
-  }
-  $ast->finish;
-}
+
+all_perl_files_ok(@dirs);
 
 done_testing;