gnu: Rename "libapr" to "apr" and "libaprutil" to "apr-util".

* gnu/packages/apr.scm: Rename file from libapr.scm.
* gnu/packages/patches/apr-skip-getservbyname-test.patch: Rename file
    from libapr-skip-getservbyname-test.patch.
* gnu-system.am (GNU_SYSTEM_MODULES): Rename module libapr to apr.
* gnu-system.am (dist_patch_DATA): Rename patch file.
* gnu/packages/apr.scm (apr): Rename from libapr.
* gnu/packages/apr.scm (apr-util): Rename from libaprutil, change
    input name.
* gnu/packages/version-control.scm (subversion): Change input name.