Revert "[test] Add paths to chrome and firefox to the environment when present"

This reverts commit 40c79c8.

Reason for revert: Breaks on windows.

Original change's description:
> [test] Add paths to chrome and firefox to the environment when present
> 
> This adds a CHROME_PATH or FIREFOX_PATH environment variable to the
> test's evnironment which contains a path to the browser's executable.
> This is only set if the --chrome or --firefox argument was passed to
> test.py.
> 
> #42417
> 
> Change-Id: I711de6ab91b8ffbbe72c7fb1530b68c4189a4b8a
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153209
> Commit-Queue: Alexander Thomas <athom@google.com>
> Reviewed-by: William Hesse <whesse@google.com>

TBR=whesse@google.com,athom@google.com

Change-Id: I7e1351f9b170ae3ddd218055efb770fe6e1f54e8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153606
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Alexander Thomas <athom@google.com>

Author: athomas

pkg/test_runner/lib/src/test_suite.dart

@@ -55,16 +55,14 @@ abstract class TestSuite {
   TestSuite(this.configuration, this.suiteName, this.statusFilePaths) {
     _environmentOverrides = {
       'DART_CONFIGURATION': configuration.configurationDirectory,
-      if (Platform.isWindows) 'DART_SUPPRESS_WER': '1',
-      if (Platform.isWindows && configuration.copyCoreDumps)
-        'DART_CRASHPAD_HANDLER':
-            Uri.base.resolve(buildDir + '/crashpad_handler.exe').toFilePath(),
-      if (configuration.chromePath != null)
-        'CHROME_PATH': Uri.base.resolve(configuration.chromePath).toFilePath(),
-      if (configuration.firefoxPath != null)
-        'FIREFOX_PATH':
-            Uri.base.resolve(configuration.firefoxPath).toFilePath(),
     };
+    if (Platform.isWindows) {
+      _environmentOverrides['DART_SUPPRESS_WER'] = '1';
+      if (configuration.copyCoreDumps) {
+        _environmentOverrides['DART_CRASHPAD_HANDLER'] =
+            Path(buildDir + '/crashpad_handler.exe').absolute.toNativePath();
+      }
+    }
   }
 
   Map<String, String> get environmentOverrides => _environmentOverrides;