Fix the bug to remove internal key when receiving the 100-continue header

[SophieGuo410]

This pr is to fix the bug that for 100-continue header support, the request will have some internal header after we handle request and send back 100-continue to customer. And in preProcessRequest we will return bad_request if any request has internal key during pre process stage. This pr is to remove those internal args for 100-continue use case specifically.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 68.18182% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 70.26%. Comparing base (52ba813) to head (8c93473). Report is 6 commits behind head on master.

Files	Patch %	Lines
...in/java/com/github/ambry/rest/MockRestRequest.java	25.00%	3 Missing :warning:
...om/github/ambry/frontend/AmbrySecurityService.java	50.00%	1 Missing and 1 partial :warning:
...java/com/github/ambry/rest/WrappedRestRequest.java	0.00%	1 Missing :warning:
...om/github/ambry/tools/perf/rest/PerfNioServer.java	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2781 +/- ## ============================================ + Coverage 64.24% 70.26% +6.02% - Complexity 10398 11682 +1284 ============================================ Files 840 840 Lines 71755 71876 +121 Branches 8611 8635 +24 ============================================ + Hits 46099 50504 +4405 + Misses 23004 18740 -4264 + Partials 2652 2632 -20 ```

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