fac1e1f qa: Remove unused option --srcdir (MarcoFalke)
Pull request description:
The `srcdir` option was both unused and misleading; It should have been called `builddir`. So remove it.
Tree-SHA512: 2c24dcf2aa82219158b8cbbf03dd3f0f51f805f1f5f670faa1fd59e5a8d60fda120ffddadeccb058d8d3f20583b4952be7afd2df6bbefb9367d35c0f0a9fda3c
Backport of Core PR13188
https://github.com/bitcoin/bitcoin/pull/13188/