libiniparser: remove unused function needing float

libiniparser: remove unused function needing float

Fixes:
|   LD      ubi-utils/ubiformat
| .../git/ubi-utils/libiniparser.a(libiniparser.o): In function
| `  LD      ubi-utils/ubirename
| iniparser_getdouble':
| .../git/ubi-utils/libiniparser.c:336: undefined reference to `atof'

Grep doesn't reveal any occurrence of iniparser_getdouble(), using atof() so
remove it: floating-point is not supported in klibc

Upstream-Status: Pending

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>