Remove deleted strings from symbols.xml.

The background activity start toast strings were removed from
strings.xml in commit 9e2457622abb8611876185f09cb79f5c3c2f4711, but
not from symbols.xml. (Because I didn't know it existed.)

Bug: 131747138
Fixes: 134686670
Test: Still builds.
Change-Id: I934e96155dcc4404f50a309f07ba4ba6c86f151f
1 file changed