remove spurious executable permissions on source code files

Fedora's rpmlint complains that some of the source code files in the tree happen to be executable. Remove the execute bits from these files to resolve the rpmlint warning.

(Explanation from rpmlint:)

```
$ rpmlint -I spurious-executable-perm
spurious-executable-perm:
The file is installed with executable permissions, but was identified as one
that probably should not be executable.  Verify if the executable bits are
desired, and remove if not.
```