webpack-loader: revert plugging-in webpack's fs to the service

it appears the inputFileSystem is not up to date on watch events, even though webpack passes in the "new" source to the loader.
should fix watch mode issues.

packages/webpack-loader/src/typescript-loader.ts

@@ -1,4 +1,3 @@
-import { dirname, join, normalize } from 'path'
 import ts from 'typescript'
 import { TypeScriptService, ITranspilationOptions } from '@ts-tools/service'
 import { resolvedModulesTransformer } from '@ts-tools/robotrix'
@@ -9,8 +8,6 @@ const { sys } = ts
 const externalSourceMapPrefix = `//# sourceMappingURL=`
 const platformHasColors = !!sys && !!sys.writeOutputIsTTY && sys.writeOutputIsTTY()
 
-const defaultLibsDirectory = dirname(ts.getDefaultLibFilePath({}))
-
 /**
  * Loader options which can be provided via webpack configuration
  * or a specific request query string
@@ -109,20 +106,7 @@ export const typescriptLoader: loader.Loader = function(/* source */) {
         tsconfigFileName: loaderOptions.tsconfigFileName,
         getCustomTransformers(_baseHost, compilerOptions) {
             return compilerOptions && compilerOptions.baseUrl ? { after: [resolvedModulesTransformer] } : undefined
-        },
-        getCustomFs: () => ({
-            // normalize paths because typescript uses linux-like path representation in Windows
-            // while webpack uses native paths
-            readFileSync: (path, encoding = 'utf8') => this.fs.readFileSync(normalize(path)).toString(encoding),
-            statSync: path => this.fs.statSync(normalize(path)),
-            readdirSync: path => this.fs.readdirSync(normalize(path)),
-            realpathSync: sys && sys.realpath,
-            dirname,
-            join,
-            normalize,
-            defaultLibsDirectory,
-            caseSensitive: !!sys && sys.useCaseSensitiveFileNames
-        })
+        }
     }
 
     // transpile using `this.resourcePath`, ignoring the `source` provided to loader.