(chore) free memory using asn1_time_free when asn1_time_set is used

[vinayakhulawale]

For consistency using time_free instead of string_free

[fffonion]

@vinayakhulawale types like ASN1_*TIME and ASN1_INTEGER are actually all stored as ASN.1 encoded string (ASN1_STRING), the types basically control different routines when parsing. For example if you want to parse the string into a integer, you pass in an ASN1_INTEGER and expect a integer to return. In fact the openssl manaul also suggests using ASN1_STRING_free on those types.
My thought will be if we want to go with this path, we should use this pattern everywhere for consistency. Considering we will likely consult openssl manual in the future, I would doubt if there's a good path to pursue
Regarding free there's no difference in each variants.

[vinayakhulawale]

@fffonion - yep, manual does say we can use ASN1_STRING_free to free memory for ASN1_TIME structure but I feel it would be more consistent to use ASN1_TIME_free when we explicitly use ASN1_TIME* .

I was checking openssl tests, they use both approaches (time_free and string_free), Libraries like luaossl sticks to time_free

[vinayakhulawale]

I am OK to close this PR, if you want to use string_free. Also if you are OK with time_free usage - I can modify script and other occurrences too.

[vinayakhulawale]

@fffonion - did you get chance to decide if you want to go with time_free or stick to string_free ?

[fffonion]

@vinayakhulawale I'll still say to use STRING_free here, let's keep in sync with manual. Thanks for your contribution!