Revert "[lldb-dap] Ensure we acquire the SB API lock while handling requests. (llvm#137026)"

Summary:
This reverts commit 3b48e2a.
Because this commit caused deadlock between DAP's main loop and the `EventThread()` who are running on different thread and could both obtain the mutex

Test Plan:
~~CI the TestDAP_reuseAdapter.py should pass~~

Guess there's no CI
```
[[email protected] ~/llvm-sand/build/Debug/fbcode-x86_64/toolchain]$ bin/llvm-lit  ~/llvm-s
and/external/llvm-project/lldb/test/API/tools/lldb-dap/reuseDAP/TestDAP_reuseAdapter.py
-- Testing: 1 tests, 1 workers --
PASS: lldb-api :: tools/lldb-dap/reuseDAP/TestDAP_reuseAdapter.py (1 of 1)

Testing Time: 7.98s

Total Discovered Tests: 1
  Passed: 1 (100.00%)
```

Rollback Plan:

Reviewers: alexandreperez, #lldb_team, peix

Reviewed By: alexandreperez

Subscribers: pdepetro, #lldb_team

Differential Revision: https://phabricator.intern.facebook.com/D78522146

Author: kusmour

lldb/tools/lldb-dap/Handler/RequestHandler.cpp

@@ -18,7 +18,6 @@
 #include "lldb/API/SBDefines.h"
 #include "lldb/API/SBEnvironment.h"
 #include "llvm/Support/Error.h"
-#include <mutex>
 
 #if !defined(_WIN32)
 #include <unistd.h>
@@ -138,9 +137,6 @@ void BaseRequestHandler::Run(const Request &request) {
     return;
   }
 
-  lldb::SBMutex lock = dap.GetAPIMutex();
-  std::lock_guard<lldb::SBMutex> guard(lock);
-
   // FIXME: After all the requests have migrated from LegacyRequestHandler >
   // RequestHandler<> we should be able to move this into
   // RequestHandler<>::operator().