Revert most of "fusefrontend: clamp oversized reads"
Revert most of "fusefrontend: clamp oversized reads"

We cannot return less data than requested to the kernel!

From https://libfuse.github.io/doxygen/structfuse__operations.html:

  Read should return exactly the number of bytes
  requested except on EOF or error, otherwise the
  rest of the data will be substituted with
  zeroes.

Reverts commit 3009ec9852316c3c696f77f476390ab5a6d8d6d7 minus
the formatting improvements we want to keep.

Fixes https://github.com/rfjakob/gocryptfs/issues/147
Reopens https://github.com/rfjakob/gocryptfs/issues/145

rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs