Revert "cpu/x86: Add function to set put_back_original_solution variable"

Now that mtrr_use_temp_range() can deal with multiple ranges there is no
need to expose this to restore the MTRR solution.

This reverts commit 00aaffaf47.

Change-Id: Ib77a0f52228cd2f19f3227824f704ac690be4aba
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/64803
Reviewed-by: Subrata Banik <subratabanik@google.com>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/x86/mtrr.h

@@ -96,7 +96,6 @@ void x86_setup_fixed_mtrrs(void);
 /* Set up fixed MTRRs but do not enable them. */
 void x86_setup_fixed_mtrrs_no_enable(void);
 void x86_mtrr_check(void);
-void need_restore_mtrr(void);
 
 /* Insert a temporary MTRR range for the duration of coreboot's runtime.
  * This function needs to be called after the first MTRR solution is derived. */