* Revert r19797, and use a simpler solution: just don't monitor build

hooks for silence.  It's unnecessary because the remote nix-store
  command is already monitoring the real build.

src/libmain/shared.cc

@@ -31,11 +31,6 @@ static void sigintHandler(int signo)
 }
 
 
-static void sigalrmHandler(int signo)
-{
-}
-
-
 Path makeRootName(const Path & gcRoot, int & counter)
 {
     counter++;
@@ -165,14 +160,6 @@ static void initAndRun(int argc, char * * argv)
     if (sigaction(SIGPIPE, &act, 0))
         throw SysError("ignoring SIGPIPE");
 
-    /* Catch SIGALRM with an empty handler (we just need it to get an
-       EINTR from blocking system calls). */
-    act.sa_handler = sigalrmHandler;
-    sigfillset(&act.sa_mask);
-    act.sa_flags = 0;
-    if (sigaction(SIGALRM, &act, 0))
-        throw SysError("installing handler for SIGALRM");
-
     /* Reset SIGCHLD to its default. */
     act.sa_handler = SIG_DFL;
     act.sa_flags = 0;