build: Remove unnecessary executables from gitian release

This removes the following executables from the binary gitian release:

- test_bitcoin-qt[.exe]
- bench_bitcoin[.exe]

@jonasschnelli and me discussed this on IRC a few days ago - unlike the
normal `bitcoin_tests` which is useful to see if it is safe to run
bitcoin on a certain OS/environment combination, there is no good reason
to include these. Better to leave them out to reduce the download
size.

Sizes from the 0.12 release:
```
2.4M bitcoin-0.12.0/bin/bench_bitcoin.exe
 22M bitcoin-0.12.0/bin/test_bitcoin-qt.exe
```

contrib/gitian-descriptors/gitian-linux.yml

@@ -25,7 +25,7 @@ files: []
 script: |
   WRAP_DIR=$HOME/wrapped
   HOSTS="i686-pc-linux-gnu x86_64-unknown-linux-gnu"
-  CONFIGFLAGS="--enable-glibc-back-compat --enable-reduce-exports LDFLAGS=-static-libstdc++"
+  CONFIGFLAGS="--enable-glibc-back-compat --enable-reduce-exports --disable-bench --disable-gui-tests LDFLAGS=-static-libstdc++"
   FAKETIME_HOST_PROGS=""
   FAKETIME_PROGS="date ar ranlib nm strip"
 

contrib/gitian-descriptors/gitian-osx.yml

@@ -29,7 +29,7 @@ files:
 script: |
   WRAP_DIR=$HOME/wrapped
   HOSTS="x86_64-apple-darwin11"
-  CONFIGFLAGS="--enable-reduce-exports GENISOIMAGE=$WRAP_DIR/genisoimage"
+  CONFIGFLAGS="--enable-reduce-exports --disable-bench --disable-gui-tests GENISOIMAGE=$WRAP_DIR/genisoimage"
   FAKETIME_HOST_PROGS=""
   FAKETIME_PROGS="ar ranlib date dmg genisoimage"
 

contrib/gitian-descriptors/gitian-win.yml

@@ -28,7 +28,7 @@ files: []
 script: |
   WRAP_DIR=$HOME/wrapped
   HOSTS="x86_64-w64-mingw32 i686-w64-mingw32"
-  CONFIGFLAGS="--enable-reduce-exports"
+  CONFIGFLAGS="--enable-reduce-exports --disable-gui-tests"
   FAKETIME_HOST_PROGS="g++ ar ranlib nm windres strip"
   FAKETIME_PROGS="date makensis zip"