STYLE: use PstreamBuffers default construct

- PstreamBuffers are nonBlocking by default, so no need to re-specify

src/functionObjects/field/DMD/DMDModels/derived/STDMD/STDMD.C

@@ -227,7 +227,7 @@ reducedKoopmanOperator()
         // the final outcome of TSQR decomposition up to sign
 
         // Don't clear storage on persistent buffer
-        PstreamBuffers pBufs(Pstream::commsTypes::nonBlocking);
+        PstreamBuffers pBufs;
         pBufs.allowClearRecv(false);
 
         const label myProcNo = Pstream::myProcNo();

src/functionObjects/field/externalCoupled/externalCoupled.C

@@ -111,7 +111,7 @@ void Foam::functionObjects::externalCoupled::readColumns
     // Get sizes for all processors
     const globalIndex globalFaces(globalIndex::gatherOnly{}, nRows);
 
-    PstreamBuffers pBufs(UPstream::commsTypes::nonBlocking);
+    PstreamBuffers pBufs;
 
     if (UPstream::master())
     {
@@ -182,7 +182,7 @@ void Foam::functionObjects::externalCoupled::readLines
     // Get sizes for all processors
     const globalIndex globalFaces(globalIndex::gatherOnly{}, nRows);
 
-    PstreamBuffers pBufs(UPstream::commsTypes::nonBlocking);
+    PstreamBuffers pBufs;
 
     if (UPstream::master())
     {

src/functionObjects/randomProcesses/energySpectrum/energySpectrum.C

@@ -215,7 +215,7 @@ bool Foam::functionObjects::energySpectrum::write()
 
     if (Pstream::parRun())
     {
-        PstreamBuffers pBufs(Pstream::commsTypes::nonBlocking);
+        PstreamBuffers pBufs;
 
         {
             UOPstream toMaster(Pstream::masterNo(), pBufs);

src/functionObjects/utilities/syncObjects/syncObjects.C

@@ -87,11 +87,7 @@ void Foam::functionObjects::syncObjects::sync()
     // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
     // Note provision of explicit all-world communicator
-    PstreamBuffers pBufs
-    (
-        UPstream::commGlobal(),
-        UPstream::commsTypes::nonBlocking
-    );
+    PstreamBuffers pBufs(UPstream::commGlobal());
 
 
     for (const int proci : pBufs.allProcs())