stbt-completion: Fix completion for `stbt templatematch`
stbt-completion: Fix completion for `stbt templatematch`

The tab-completion script was trying to read the possible `match_method`
and `confirm_method` values from the `stbt-templatematch` GStreamer
element, which hasn't existed since 0f0dc1a6, 7 months ago.

I suppose I *could* somehow parse these from `man stbt`, but it doesn't
seem worth the effort. I'll just enter them literally; changing those
values would break user scripts, so they are unlikely to change.

martynjarvis/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,stb-tester/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,LewisHaley/stb-tester,wmanley/stb-tester,LewisHaley/stb-tester,LewisHaley/stb-tester,martynjarvis/stb-tester,martynjarvis/stb-tester,stb-tester/stb-tester,martynjarvis/stb-tester,wmanley/stb-tester