cmd-export: Remove reference to MySQL and PostgreSQL

ReviewDb is gone, hence MySQL and PostgreSQL are no longer used.

Change-Id: I2fa3ad412522c63ee71e2f8df073afc13fabe463
Signed-off-by: Edwin Kempin <ekempin@google.com>

src/main/resources/Documentation/cmd-export.md

diff --git a/src/main/resources/Documentation/cmd-export.md b/src/main/resources/Documentation/cmd-export.md
index 011e51a..1472578 100644
--- a/src/main/resources/Documentation/cmd-export.md
+++ b/src/main/resources/Documentation/cmd-export.md
@@ -19,8 +19,7 @@
 each merged change.
 
 This task can take quite some time, but can run in the background
-concurrently to the server if the database is MySQL or PostgreSQL.
-If the database is H2, this task must be run by itself.
+concurrently to the server.
 
 ACCESS
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