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 ⚠️
...om/github/ambry/frontend/AmbrySecurityService.java	50.00%	1 Missing and 1 partial ⚠️
...java/com/github/ambry/rest/WrappedRestRequest.java	0.00%	1 Missing ⚠️
...om/github/ambry/tools/perf/rest/PerfNioServer.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             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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