Fix compiler warning in LIEF::BinaryStream::peek_u16string()
Fix compiler warning in LIEF::BinaryStream::peek_u16string()

This change fixes this compiler warning:

```sh
[218/228] Building CXX object vendor/lief/CMakeFiles/LIB_LIEF.dir/src/BinaryStream/BinaryStream.cpp.o
/Users/raisinten/Desktop/git/postject/vendor/lief/src/BinaryStream/BinaryStream.cpp:232:10: warning: variable 'count' set but not used [-Wunused-but-set-variable]
  size_t count = 0;
         ^
1 warning generated.
```

by removing all uses of count because it is unused.

Signed-off-by: Darshan Sen <c66f01d33aca0f91e762bdaf4b23b204f4939502@gmail.com>

lief-project/LIEF,lief-project/LIEF,lief-project/LIEF,lief-project/LIEF