refactor: removed unused option hmr (#608)

Author: cap-Bernardito

src/loader-options.json

@@ -15,9 +15,6 @@
     "esModule": {
       "type": "boolean"
     },
-    "hmr": {
-      "type": "boolean"
-    },
     "modules": {
       "type": "object",
       "additionalProperties": false,

test/__snapshots__/validate-loader-options.test.js.snap

@@ -5,11 +5,6 @@ exports[`validate options should throw an error on the "esModule" option with "1
  - options.esModule should be a boolean."
 `;
 
-exports[`validate options should throw an error on the "hmr" option with "1" value 1`] = `
-"Invalid options object. Mini CSS Extract Plugin Loader has been initialized using an options object that does not match the API schema.
- - options.hmr should be a boolean."
-`;
-
 exports[`validate options should throw an error on the "modules" option with "{"namedExport":"false"}" value 1`] = `
 "Invalid options object. Mini CSS Extract Plugin Loader has been initialized using an options object that does not match the API schema.
  - options.modules.namedExport should be a boolean.

test/validate-loader-options.test.js

@@ -10,10 +10,6 @@ describe('validate options', () => {
       success: [true, false],
       failure: [1],
     },
-    hmr: {
-      success: [true, false],
-      failure: [1],
-    },
     modules: {
       success: [{ namedExport: true }, { namedExport: false }],
       failure: ['true', { namedExport: 'false' }],