Remove unnecessary code: was When generating constructor, trim known prefixes...

Remove unnecessary code: was When generating constructor, trim known prefixes from argument name to get parameter name  (#34804)

* Fixes #33673

* Respond to feedback

* Remove unneeded code and add tests

* Fix access modifier

src/EditorFeatures/CSharpTest/GenerateConstructor/GenerateConstructorTests.cs

@@ -3676,5 +3676,43 @@ class D
 {
 }", options: options.MergeStyles(options.FieldNamesAreCamelCaseWithUnderscore, options.ParameterNamesAreCamelCaseWithPUnderscorePrefix, LanguageNames.CSharp));
         }
+
+        [WorkItem(33673, "https://github.com/dotnet/roslyn/issues/33673")]
+        [Theory, Trait(Traits.Feature, Traits.Features.CodeActionsGenerateConstructor)]
+        [InlineData("_s", "s")]
+        [InlineData("_S", "s")]
+        [InlineData("m_s", "s")]
+        [InlineData("m_S", "s")]
+        [InlineData("s_s", "s")]
+        [InlineData("t_s", "s")]
+        public async Task GenerateConstructor_ArgumentHasCommonPrefix(string argumentName, string fieldName)
+        {
+            await TestInRegularAndScriptAsync(
+$@"
+class Program
+{{
+    static void Main(string[] args)
+    {{
+        string {argumentName} = "";
+        new Prog[||]ram({argumentName});
+    }}
+}}",
+$@"
+class Program
+{{
+    private string {fieldName};
+
+    public Program(string {fieldName})
+    {{
+        this.{fieldName} = {fieldName};
+    }}
+
+    static void Main(string[] args)
+    {{
+        string {argumentName} = "";
+        new Program({argumentName});
+    }}
+}}");
+        }
     }
 }

src/Workspaces/Core/Portable/Utilities/ParameterName.cs

@@ -51,9 +51,7 @@ public ParameterName(string nameBasedOnArgument, bool isFixed, NamingRule parame
             {
                 // Otherwise, massage it a bit to be a more suitable match for
                 // how people actually writing parameters.
-                var trimmed = nameBasedOnArgument.TrimStart('_');
-                BestNameForParameter = trimmed.Length > 0 ? trimmed.ToCamelCase() : nameBasedOnArgument;
-                BestNameForParameter = parameterNamingRule.NamingStyle.MakeCompliant(BestNameForParameter).First();
+                BestNameForParameter = parameterNamingRule.NamingStyle.MakeCompliant(nameBasedOnArgument).First();
             }
         }