drivers: timer: remove reset release for lptim

The LL_APBx_GRPn_ReleaseReset clears reset bit in RCC,
however this bit is reset by default. Code that set
this bit was removed in previous commit
0856e991
Keepint the autonomous clocks for STM32U5 family.

Signed-off-by: Adam Berlinger <adam.berlinger@st.com>