Address PR feedback from dotnet#2579

We don't need a TryConvert method, we already have a TryParse, which can be used instead.

Author: eerhardt

src/Microsoft.ML.Data/Data/Conversion.cs

@@ -1585,17 +1585,6 @@ public void Convert(in TX span, ref I4 value)
         {
             value = ParseI4(in span);
         }
-        public bool TryConvert(in TX span, ref I4 value)
-        {
-            TryParseSigned(I4.MaxValue, in span, out long? res);
-            if (res.HasValue)
-            {
-                value = (I4)res.GetValueOrDefault();
-                return true;
-            }
-
-            return false;
-        }
         public void Convert(in TX span, ref U4 value)
         {
             value = ParseU4(in span);

src/Microsoft.ML.Data/DataLoadSave/Text/TextLoaderParser.cs

@@ -1016,8 +1016,8 @@ public int GatherFields(ReadOnlyMemory<char> lineSpan, ReadOnlySpan<char> span,
                                 }
                                 var spanT = Fields.Spans[Fields.Count - 1];
 
-                                int csrc = 0;
-                                if (!Conversions.Instance.TryConvert(in spanT, ref csrc) || csrc <= 0)
+                                int csrc;
+                                if (!Conversions.Instance.TryParse(in spanT, out csrc) || csrc <= 0)
                                 {
                                     _stats.LogBadFmt(ref scan, "Bad dimensionality or ambiguous sparse item. Use sparse=- for non-sparse file, and/or quote the value.");
                                     break;