This reverts commit 46d6aa520f.
Since commit 7c60211ce3 (tslib: needs kernel headers 3.12)
BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_12 is always enabled when building tslib. No
need to check for that.
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>