build: workaround for 'realpath' missing on macOS

contrib/osx/base.sh

@@ -21,7 +21,3 @@ function DoCodeSignMaybe { # ARGS: infoName fileOrDirName codesignIdentity
     info "Code signing ${infoName}..."
     codesign -f -v $deep -s "$identity" "$file" || fail "Could not code sign ${infoName}"
 }
-
-function realpath() {
-    [[ $1 = /* ]] && echo "$1" || echo "$PWD/${1#./}"
-}