enums: omit trailing comma for portability

enums: omit trailing comma for portability

Since v1.7.2-rc0~23^2~2 (Add per-repository eol normalization,
2010-05-19), building with gcc -std=gnu89 -pedantic produces warnings
like the following:

 convert.c:21:11: warning: comma at end of enumerator list [-pedantic]

gcc is right to complain --- these commas are not permitted in C89.
In the spirit of v1.7.2-rc0~32^2~16 (2010-05-14), remove them.

Signed-off-by: Jonathan Nieder <redacted>
Signed-off-by: Junio C Hamano <redacted>