xbps-src: multiple changes to improve infrastructure.

- Remove buildvars_funcs.sh, its code has been moved into set_tmpl_common_vars().
- Move stripping code into its own file, and don't run it via fakeroot.
- Remove unnecesary reset_tmpl_vars() call in install_pkg().
- Misc changes.

xbps-src/shutils/build_funcs.sh

@@ -74,9 +74,6 @@ build_src_phase()
 		fi
 	fi
 
-	. $XBPS_SHUTILSDIR/buildvars_funcs.sh
-	set_build_vars
-
 	msg_normal "Package '$pkgname ($lver)': running build phase."
 
 	if [ "$build_style" = "custom-install" ]; then
@@ -109,7 +106,6 @@ build_src_phase()
 	fi
 
 	unset makejobs
-	unset_build_vars
 
 	touch -f $XBPS_BUILD_DONE
 }