[llvm-exegesis] Remove unused Counter::read method (#76651)

This method was simply a wrapper around readOrError. All users within
the llvm-exegesis code base should have been processing an actual error
rather than using the wrapper. This patch removes the wrapper and
rewrites the users (just 1) to use the readOrError method.

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

@@ -356,7 +356,11 @@ class SubProcessFunctionExecutorImpl
       if (ChildExitCode == 0) {
         // The child exited succesfully, read counter values and return
         // success
-        CounterValues[0] = Counter->read();
+        auto CounterValueOrErr = Counter->readOrError();
+        if (!CounterValueOrErr)
+          return CounterValueOrErr.takeError();
+        CounterValues = std::move(*CounterValueOrErr);
+
         return Error::success();
       }
       // The child exited, but not successfully

llvm/tools/llvm-exegesis/lib/PerfHelper.cpp

@@ -148,17 +148,6 @@ void Counter::stop() {
     ioctl(FileDescriptor, PERF_EVENT_IOC_DISABLE, 0);
 }
 
-int64_t Counter::read() const {
-  auto ValueOrError = readOrError();
-  if (ValueOrError) {
-    if (!ValueOrError.get().empty())
-      return ValueOrError.get()[0];
-    errs() << "Counter has no reading\n";
-  } else
-    errs() << ValueOrError.takeError() << "\n";
-  return -1;
-}
-
 llvm::Expected<llvm::SmallVector<int64_t, 4>>
 Counter::readOrError(StringRef /*unused*/) const {
   int64_t Count = 0;
@@ -187,8 +176,6 @@ void Counter::start() {}
 
 void Counter::stop() {}
 
-int64_t Counter::read() const { return 42; }
-
 llvm::Expected<llvm::SmallVector<int64_t, 4>>
 Counter::readOrError(StringRef /*unused*/) const {
   if (IsDummyEvent) {

llvm/tools/llvm-exegesis/lib/PerfHelper.h

@@ -95,9 +95,6 @@ class Counter {
   /// Stops the measurement of the event.
   void stop();
 
-  /// Returns the current value of the counter or -1 if it cannot be read.
-  int64_t read() const;
-
   /// Returns the current value of the counter or error if it cannot be read.
   /// FunctionBytes: The benchmark function being executed.
   /// This is used to filter out the measurements to ensure they are only