tests: skip some tests when using simple store

generaldelta is a revlog implementation detail. We don't need to
test it with the simple store.

union repos are heavily revlog based. It should be possible to
run them with alternate stores. But it's not worth the trouble
at this juncture.

Differential Revision: https://phab.mercurial-scm.org/D3040

tests/test-generaldelta.t

@@ -1,3 +1,5 b''
+#require no-reposimplestore
+
 Check whether size of generaldelta revlog is not bigger than its
 regular equivalent. Test would fail if generaldelta was naive
 implementation of parentdelta: third manifest revision would be fully

tests/test-unionrepo.t

@@ -1,3 +1,5 b''
+#require no-reposimplestore
+
 Test unionrepo functionality
 
 Create one repository