Fix unused-return in proxygen/lib/http/codec/ErrorCode.cpp +2

Summary:
LLVM has a warning `-Wunreachable-code-return` which identifies return statements that cannot be reached.

In innocuous situations such statements are often present:
* to satisfy a compiler warning that existed before `[[noreturn]]` was introduced. Now that we have `[[noreturn]]`, this use is not necessary.
* to specify a return type. But there are clearer ways to do this.
* in place of the more legible `__builtin_unreachable()` (which will soon become `std::unreachable()`). In this case, we should use the more legible alternative.
* because the programmer was afraid of the function unexpectedly returning. But we check for this condition with `-Wreturn-type`.

In dangerous situations such statements can obscure the intended execution of the program or even hide an erroneous early return.

In this diff, we remove one or more unreachable returns.

 - If you approve of this diff, please use the "Accept & Ship" button :-)

Differential Revision: D77424525

fbshipit-source-id: 41b3b0350e5de1ac7a4c9a3a06d5d2e3d9203f16

Author: r-barnes

third-party/proxygen/src/proxygen/lib/http/codec/ErrorCode.cpp

@@ -46,7 +46,6 @@ const char* getErrorCodeString(ErrorCode error) {
       return "MAX";
   }
   LOG(FATAL) << "Unreachable";
-  return "";
 }
 
 } // namespace proxygen