Fix an enum comparison that was blowing up jenkins.

[asn-d6]

The warning was:
11:23:10 ../tor/src/feature/hs/hs_service.c: In function 'log_cant_upload_desc':
11:23:10 ../tor/src/feature/hs/hs_service.c:3118:3: error: comparison of unsigned expression < 0 is always false [-Werror=type-limits]
See #34254 for more info.

I guess this means that gcc assigned an unsigned type to the
log_desc_upload_reason_t enum and it warned if we compared it against 0...

For now I think it's simpler to remove that check instead of turning the enum
to a signed type, or trying to hack it some other way.

From what it seems, enum is up to the compiler on whether it's signed/unsigned:
https://stackoverflow.com/questions/159034/are-c-enums-signed-or-unsigned

[coveralls]

Pull Request Test Coverage Report for Build 8981

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 64.217%

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Files with Coverage Reduction	New Missed Lines	%
src/feature/hs/hs_common.c	1	84.48%

Totals
Change from base Build 8974:	0.02%
Covered Lines:	50945
Relevant Lines:	79333

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💛 - Coveralls