Removed String.startsWith !FABLE_COMPILER condition (#611)

* Removed String.startsWith FABLE_COMPILER condition

* Fable updated to 4.23.0

Author: laurentpayot

.config/dotnet-tools.json

@@ -3,7 +3,7 @@
   "isRoot": true,
   "tools": {
     "fable": {
-      "version": "4.5.0",
+      "version": "4.23.0",
       "commands": [
         "fable"
       ]

src/FSharpPlus/Extensions/String.fs

@@ -52,8 +52,6 @@ module String =
 
         source.Contains subString
 
-    #if !FABLE_COMPILER
-    
     /// Does the source string start with the given subString? -- function wrapper for String.StartsWith method using InvariantCulture.
     let startsWith (subString: string) (source: string) =
         #if !NET45
@@ -62,7 +60,6 @@ module String =
         #endif
 
         source.StartsWith (subString, false, CultureInfo.InvariantCulture)
-    #endif
 
     /// Does the source string end with the given subString? -- function wrapper for String.EndsWith method using InvariantCulture.
     let endsWith subString (source: string) =