Revert "Bug/allow header to contain http verb keys #1252 (#1258)" (#2977)

This reverts commit 920510b3a6.

lib/core/dispatchRequest.js

@@ -43,9 +43,7 @@ module.exports = function dispatchRequest(config) {
   utils.forEach(
     ['delete', 'get', 'head', 'post', 'put', 'patch', 'common'],
     function cleanHeaderConfig(method) {
-      if (typeof config.headers[method] !== 'string') {
+      delete config.headers[method];
-        delete config.headers[method];
-      }
     }
   );
 

test/specs/headers.spec.js

@@ -86,17 +86,4 @@ describe('headers', function () {
       done();
     });
   });
-
-  describe('when a header key matches an HTTP verb', function() {
-    it('preserves the header value', function(done) {
-      axios.post('/foo', null, { 'headers': { 'delete': 'test' } });
-
-      getAjaxRequest().then(function (request) {
-        var headerValue = request.requestHeaders['delete'];
-
-        expect(headerValue).toEqual('test');
-        done();
-      });
-    });
-  });
 });