[Offload][OpenMP] remove SourceInfo::removePath (#226283)

Following discussion on
https://discourse.llvm.org/t/rfc-add-opt-in-option-for-full-source-paths-in-offload-info-output/91901
this commit removes SourceInfo::removePath which changes
LIBOMPTARGET_INFO to provide a non truncated source path:

``` c
#include <stdio.h>

#define N 4

int main(void) {
  int a[N];
  for (int i = 0; i < N; ++i)
    a[i] = 0;
#pragma omp target map(tofrom : a[0 : N])
  {
    a[0] = 1;
  }
  printf("%d\n", a[0]); /* expect 1 */
  return 0;
}
```

``` bash
clang -fopenmp -fopenmp-targets=amdgcn-amd-amdhsa -g ./test/test.c

# new
LIBOMPTARGET_INFO=-1 ./a.out
omptarget device 0 info: Entering OpenMP kernel at ./test/test.c:9:1 with 1 arguments:

# old
LIBOMPTARGET_INFO=-1 ./a.out
omptarget device 0 info: Entering OpenMP kernel at test.c:9:1 with 1 arguments:
```
GitOrigin-RevId: 5b8e65685b4fe99191a217bfa0527c51cf36925c