* gnu/packages/emulators.scm (retroarch): Update to 1.15.0.
[source]: Remove upstreamed patch.
[arguments]<#:phases>: Remove not needed changes for 'true' and 'zlib'.
Remove "--disable-builtinminiupnpc" from configure flags.
Add "--disable-builtinzlib" to configure flags.
[inputs]: Remove miniupnpc, which is not used any more.
* gnu/packages/patches/retroarch-LIBRETRO_DIRECTORY: Remove file.
* gnu/local.mk (dist_patch_DATA): Remove it.