Remove no-op stream capture around javac call

We fork a process with a process logger that redirects
stdout and stderr to a log file, so I can't see why this
was ever needed.

Tested:

```
Note: test execution will be non-parallel under -Dpartest.exec.in.process
% scalac t1459/InheritingPrinter.scala t1459/JavaPrinter.java t1459/ScalaPrinter.scala t1459/Test.java t1459/VarArg.java
!! 1 - run/t1459                                 [compilation failed]

% scalac t1459/InheritingPrinter.scala t1459/JavaPrinter.java t1459/ScalaPrinter.scala t1459/Test.java t1459/VarArg.java
JavaPrinter.java:1: error: illegal start of type declaration
public cla ss JavaPrinter implements VarArg {
           ^
one error found

partest --update-check \
  /Users/jz/code/scala/test/files/run/t1459
```

Author: retronym

src/main/scala/scala/tools/partest/nest/Runner.scala

@@ -131,9 +131,7 @@ class Runner(val testFile: File, val suiteRunner: SuiteRunner, val nestUI: NestU
     )
 
     pushTranscript(args mkString " ")
-    val captured = StreamCapture(runCommand(args, logFile))
-    if (captured.result) genPass() else {
-      logFile appendAll captured.stderr
+    if (runCommand(args, logFile)) genPass() else {
       genFail("java compilation failed")
     }
   }

src/main/scala/scala/tools/partest/nest/StreamCapture.scala

@@ -9,23 +9,6 @@ import java.io.{Console => _, _}
 import java.nio.charset.Charset
 
 object StreamCapture {
-  case class Captured[T](stdout: String, stderr: String, result: T) {
-    override def toString = s"""
-      |result: $result
-      |[stdout]
-      |$stdout
-      |[stderr]
-      |$stderr""".stripMargin.trim
-  }
-
-  private def mkStream = {
-    val swr     = new StringWriter
-    val wr      = new PrintWriter(swr, true)
-    val ostream = new PrintStream(new OutputStream { def write(b: Int): Unit = wr write b }, true) // autoFlush = true
-
-    (ostream, () => { ostream.close() ; swr.toString })
-  }
-
   def savingSystem[T](body: => T): T = {
     val savedOut  = System.out
     val savedErr  = System.err
@@ -36,22 +19,6 @@ object StreamCapture {
     }
   }
 
-  def apply[T](body: => T): Captured[T] = {
-    val (outstream, stdoutFn) = mkStream
-    val (errstream, stderrFn) = mkStream
-
-    val result = savingSystem {
-      System setOut outstream
-      System setErr errstream
-      Console.withOut(outstream) {
-        Console.withErr(errstream) {
-          body
-        }
-      }
-    }
-    Captured(stdoutFn(), stderrFn(), result)
-  }
-
   def capturingOutErr[A](output: OutputStream)(f: => A): A = {
     import java.io._
     val charset = Charset.defaultCharset()