Kernel: Don't interrupt short writes

Remove explicit checking for pending signals from writing code paths,
since this is handled automatically when blocking, and should not
happen if the write() call is "short", i.e. doesn't block. All the
other syscalls already work like this.

Fixes https://github.com/SerenityOS/serenity/issues/797

Kernel/Process.cpp

@@ -1072,13 +1072,6 @@ ssize_t Process::sys$writev(int fd, const struct iovec* iov, int iov_count)
         nwritten += rc;
     }
 
-    if (current->has_unmasked_pending_signals()) {
-        if (current->block<Thread::SemiPermanentBlocker>(Thread::SemiPermanentBlocker::Reason::Signal) == Thread::BlockResult::InterruptedBySignal) {
-            if (nwritten == 0)
-                return -EINTR;
-        }
-    }
-
     return nwritten;
 }
 
@@ -1121,12 +1114,6 @@ ssize_t Process::do_write(FileDescription& description, const u8* data, int data
         }
         if (rc == 0)
             break;
-        if (current->has_unmasked_pending_signals()) {
-            if (current->block<Thread::SemiPermanentBlocker>(Thread::SemiPermanentBlocker::Reason::Signal) == Thread::BlockResult::InterruptedBySignal) {
-                if (nwritten == 0)
-                    return -EINTR;
-            }
-        }
         nwritten += rc;
     }
     return nwritten;
@@ -1146,14 +1133,8 @@ ssize_t Process::sys$write(int fd, const u8* data, ssize_t size)
     auto* description = file_description(fd);
     if (!description)
         return -EBADF;
-    auto nwritten = do_write(*description, data, size);
-    if (current->has_unmasked_pending_signals()) {
-        if (current->block<Thread::SemiPermanentBlocker>(Thread::SemiPermanentBlocker::Reason::Signal) == Thread::BlockResult::InterruptedBySignal) {
-            if (nwritten == 0)
-                return -EINTR;
-        }
-    }
-    return nwritten;
+
+    return do_write(*description, data, size);
 }
 
 ssize_t Process::sys$read(int fd, u8* buffer, ssize_t size)